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C++ Programming Code Examples

C++ > Data Structures and Algorithm Analysis in C++ Code Examples

If you don't have a string type

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/* If you don't have a string type */ #include <string.h> #include "mystring.h" string::string( const char * cstring ) { if( cstring == NULL ) cstring = ""; strLength = strlen( cstring ); bufferLength = strLength + 1; buffer = new char[ bufferLength ]; strcpy( buffer, cstring ); } string::string( const string & str ) { strLength = str.length( ); bufferLength = strLength + 1; buffer = new char[ bufferLength ]; strcpy( buffer,str.buffer ); } const string & string::operator=( const string & rhs ) { if( this != &rhs ) { if( bufferLength < rhs.length( ) + 1 ) { delete [ ] buffer; bufferLength = rhs.length( ) + 1; buffer = new char[ bufferLength ]; } strLength = rhs.length( ); strcpy( buffer, rhs.buffer ); } return *this; } const string & string::operator+=( const string & rhs ) { if( this == &rhs ) { string copy( rhs ); return *this += copy; } int newLength = length( ) + rhs.length( ); if( newLength >= bufferLength ) { bufferLength = 2 * ( newLength + 1 ); char *oldBuffer = buffer; buffer = new char[ bufferLength ]; strcpy( buffer, oldBuffer ); delete [ ] oldBuffer; } strcpy( buffer + length( ), rhs.buffer ); strLength = newLength; return *this; } char & string::operator[ ]( int k ) { if( k < 0 || k >= strLength ) throw StringIndexOutOfBounds( ); return buffer[ k ]; } char string::operator[ ]( int k ) const { if( k < 0 || k >= strLength ) throw StringIndexOutOfBounds( ); return buffer[ k ]; } ostream & operator<<( ostream & out, const string & str ) { return out << str.c_str(); } istream & operator>>( istream & in, string & str ) { char buf[ string::MAX_LENGTH + 1 ]; in >> buf; if( !in.fail( ) ) str = buf; return in; } istream & getline( istream & in, string & str ) { char buf[ string::MAX_LENGTH + 1 ]; in.getline( buf, string::MAX_LENGTH ); if( !in.fail( ) ) str = buf; return in; } bool operator==( const string & lhs, const string & rhs ) { return strcmp( lhs.c_str( ), rhs.c_str( ) ) == 0; } bool operator!=( const string & lhs, const string & rhs ) { return strcmp( lhs.c_str( ), rhs.c_str( ) ) != 0; } bool operator<( const string & lhs, const string & rhs ) { return strcmp( lhs.c_str( ), rhs.c_str( ) ) < 0; } bool operator<=( const string & lhs, const string & rhs ) { return strcmp( lhs.c_str( ), rhs.c_str( ) ) <= 0; } bool operator>( const string & lhs, const string & rhs ) { return strcmp( lhs.c_str( ), rhs.c_str( ) ) > 0; } bool operator>=( const string & lhs, const string & rhs ) { return strcmp( lhs.c_str( ), rhs.c_str( ) ) >= 0; }
If Else If Ladder in C/C++
The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities. The if...else ladder allows you to check between multiple test expressions and execute different statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax of if...else Ladder in C++
if (Condition1) { Statement1; } else if(Condition2) { Statement2; } . . . else if(ConditionN) { StatementN; } else { Default_Statement; }
In the above syntax of if-else-if, if the Condition1 is TRUE then the Statement1 will be executed and control goes to next statement in the program following if-else-if ladder. If Condition1 is FALSE then Condition2 will be checked, if Condition2 is TRUE then Statement2 will be executed and control goes to next statement in the program following if-else-if ladder. Similarly, if Condition2 is FALSE then next condition will be checked and the process continues. If all the conditions in the if-else-if ladder are evaluated to FALSE, then Default_Statement will be executed.
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/* write a C program which demonstrate use of if-else-if ladder statement */ /* Program to Print Day Names using Else If Ladder in C++*/ #include <iostream> using namespace std; int main() { int day; cout << "Enter Day Number: "; cin >> day; cout << "Day is "; if (day == 1) cout << "Sunday" << endl; else if (day == 2) cout << "Monday" << endl; else if (day == 3) cout << "Tuesday" << endl; else if (day == 4) cout << "Wednesday" << endl; else if (day == 5) cout << "Thursday" << endl; else if (day == 6) cout << "Friday" << endl; else cout << "Saturday" << endl; return 0; }
IOS Library fail() Function in C++
Check whether either failbit or badbit is set. Returns true if either (or both) the failbit or the badbit error state flags is set for the stream. At least one of these flags is set when an error occurs during an input operation. failbit is generally set by an operation when the error is related to the internal logic of the operation itself; further operations on the stream may be possible. While badbit is generally set when the error involves the loss of integrity of the stream, which is likely to persist even if a different operation is attempted on the stream. badbit can be checked independently by calling member function bad.
Syntax for IOS fail() Function in C++
bool fail() const;
This function does not accept any parameter. Function returns true if badbit and/or failbit are set. false otherwise. iostate value indicates functions to check state flags (member constant) good() eof() fail() bad() rdstate() goodbit No errors (zero value iostate) true false false false goodbit eofbit End-of-File reached on input operation false true false false eofbit failbit Logical error on i/o operation false false true false failbit badbit Read/writing error on i/o operation false false true true badbit eofbit, failbit and badbit are member constants with implementation-defined values that can be combined (as if with the bitwise OR operator). goodbit is zero, indicating that none of the other bits is set. Reaching the End-of-File sets the eofbit. But note that operations that reach the End-of-File may also set the failbit if this makes them fail (thus setting both eofbit and failbit). This function is a synonym of ios::operator!.
Data races
Accesses the stream object. Concurrent access to the same stream object may cause data races.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the stream.
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/* The fail() method of ios class in C++ is used to check if the stream is has raised any fail error. It means that this function will check if this stream has its failbit set. */ /* check whether either failbit or badbit is set by ios::fail function code example */ #include <iostream> #include <fstream> #include <cstdlib> int main() { std::ifstream file("test.txt"); if(!file) // operator! is used here { std::cout << "File opening failed\n"; return EXIT_FAILURE; } // typical C++ I/O loop uses the return value of the I/O function // as the loop controlling condition, operator bool() is used here for(int n; file >> n; ) { std::cout << n << ' '; } std::cout << '\n'; if (file.bad()) std::cout << "I/O error while reading\n"; else if (file.eof()) std::cout << "End of file reached successfully\n"; else if (file.fail()) std::cout << "Non-integer data encountered\n"; }
Memory Management new Operator in C++
Allocate storage space. Default allocation functions (single-object form). A new operator is used to create the object while a delete operator is used to delete the object. When the object is created by using the new operator, then the object will exist until we explicitly use the delete operator to delete the object. Therefore, we can say that the lifetime of the object is not related to the block structure of the program.
Syntax for new Operator in C++
#include <new> //throwing (1) void* operator new (std::size_t size); //nothrow (2) void* operator new (std::size_t size, const std::nothrow_t& nothrow_value) noexcept; //placement (3) void* operator new (std::size_t size, void* ptr) noexcept;
size
Size in bytes of the requested memory block. This is the size of the type specifier in the new-expression when called automatically by such an expression. If this argument is zero, the function still returns a distinct non-null pointer on success (although dereferencing this pointer leads to undefined behavior). size_t is an integral type.
nothrow_value
The constant nothrow. This parameter is only used to distinguish it from the first version with an overloaded version. When the nothrow constant is passed as second parameter to operator new, operator new returns a null-pointer on failure instead of throwing a bad_alloc exception. nothrow_t is the type of constant nothrow.
ptr
A pointer to an already-allocated memory block of the proper size. If called by a new-expression, the object is initialized (or constructed) at this location. For the first and second versions, function returns a pointer to the newly allocated storage space. For the third version, ptr is returned. • (1) throwing allocation: Allocates size bytes of storage, suitably aligned to represent any object of that size, and returns a non-null pointer to the first byte of this block. On failure, it throws a bad_alloc exception. • (2) nothrow allocation: Same as above (1), except that on failure it returns a null pointer instead of throwing an exception. The default definition allocates memory by calling the the first version: ::operator new (size). If replaced, both the first and second versions shall return pointers with identical properties. • (3) placement: Simply returns ptr (no storage is allocated). Notice though that, if the function is called by a new-expression, the proper initialization will be performed (for class objects, this includes calling its default constructor). The default allocation and deallocation functions are special components of the standard library; They have the following unique properties: • Global: All three versions of operator new are declared in the global namespace, not within the std namespace. • Implicit: The allocating versions ((1) and (2)) are implicitly declared in every translation unit of a C++ program, no matter whether header <new> is included or not. • Replaceable: The allocating versions ((1) and (2)) are also replaceable: A program may provide its own definition that replaces the one provided by default to produce the result described above, or can overload it for specific types. If set_new_handler has been used to define a new_handler function, this new-handler function is called by the default definitions of the allocating versions ((1) and (2)) if they fail to allocate the requested storage. operator new can be called explicitly as a regular function, but in C++, new is an operator with a very specific behavior: An expression with the new operator, first calls function operator new (i.e., this function) with the size of its type specifier as first argument, and if this is successful, it then automatically initializes or constructs the object (if needed). Finally, the expression evaluates as a pointer to the appropriate type.
Data races
Modifies the storage referenced by the returned value. Calls to allocation and deallocation functions that reuse the same unit of storage shall occur in a single total order where each deallocation happens entirely before the next allocation. This shall also apply to the observable behavior of custom replacements for this function.
Exception safety
The first version (1) throws bad_alloc if it fails to allocate storage. Otherwise, it throws no exceptions (no-throw guarantee).
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/* C++ allows us to allocate the memory of a variable or an array in run time. This is known as dynamic memory allocation. The new operator denotes a request for memory allocation on the Free Store. If sufficient memory is available, new operator initializes the memory and returns the address of the newly allocated and initialized memory to the pointer variable. */ /* Allocate storage space by operator new */ // C++ program code example to illustrate dynamic allocation and deallocation of memory using new and delete #include <iostream> using namespace std; int main () { // Pointer initialization to null int* p = NULL; // Request memory for the variable // using new operator p = new(nothrow) int; if (!p) cout << "allocation of memory failed\n"; else { // Store value at allocated address *p = 29; cout << "Value of p: " << *p << endl; } // Request block of memory // using new operator float *r = new float(75.25); cout << "Value of r: " << *r << endl; // Request block of memory of size n int n = 5; int *q = new(nothrow) int[n]; if (!q) cout << "allocation of memory failed\n"; else { for (int i = 0; i < n; i++) q[i] = i+1; cout << "Value store in block of memory: "; for (int i = 0; i < n; i++) cout << q[i] << " "; } // freed the allocated memory delete p; delete r; // freed the block of allocated memory delete[] q; return 0; }
Strings in C++ Language
Strings are objects that represent sequences of characters. The standard string class provides support for such objects with an interface similar to that of a standard container of bytes, but adding features specifically designed to operate with strings of single-byte characters. The string class is an instantiation of the basic_string class template that uses char (i.e., bytes) as its character type, with its default char_traits and allocator types. Note that this class handles bytes independently of the encoding used: If used to handle sequences of multi-byte or variable-length characters (such as UTF-8), all members of this class (such as length or size), as well as its iterators, will still operate in terms of bytes (not actual encoded characters).
Declaration for Strings in C++
char str[4] = "C++ Programming"; char str[] = {'C','+','+','\0'}; char str[4] = {'C','+','+','\0'};
In C programming, the collection of characters is stored in the form of arrays. This is also supported in C++ programming. Hence it's called C-strings. C-strings are arrays of type char terminated with null character, that is, \0 (ASCII value of null character is 0). • A character array is simply an array of characters that can be terminated by a null character. A string is a class that defines objects that be represented as a stream of characters. • The size of the character array has to be allocated statically, more memory cannot be allocated at run time if required. Unused allocated memory is wasted in the case of the character array. In the case of strings, memory is allocated dynamically. More memory can be allocated at run time on demand. As no memory is preallocated, no memory is wasted. • There is a threat of array decay in the case of the character array. As strings are represented as objects, no array decay occurs. • Implementation of character array is faster than std:: string. Strings are slower when compared to implementation than character array. • Character arrays do not offer many inbuilt functions to manipulate strings. String class defines a number of functionalities that allow manifold operations on strings.
String Functions in C++
• int compare(const string& str): It is used to compare two string objects. • int length(): It is used to find the length of the string. • void swap(string& str): It is used to swap the values of two string objects. • string substr(int pos,int n): It creates a new string object of n characters. • int size(): It returns the length of the string in terms of bytes. • void resize(int n): It is used to resize the length of the string up to n characters. • string& replace(int pos,int len,string& str): It replaces portion of the string that begins at character position pos and spans len characters. • string& append(const string& str): It adds new characters at the end of another string object. • char& at(int pos): It is used to access an individual character at specified position pos. • int find(string& str,int pos,int n): It is used to find the string specified in the parameter. • int find_first_of(string& str,int pos,int n): It is used to find the first occurrence of the specified sequence. • int find_first_not_of(string& str,int pos,int n ): It is used to search the string for the first character that does not match with any of the characters specified in the string. • int find_last_of(string& str,int pos,int n): It is used to search the string for the last character of specified sequence. • int find_last_not_of(string& str,int pos): It searches for the last character that does not match with the specified sequence. • string& insert(): It inserts a new character before the character indicated by the position pos. • int max_size(): It finds the maximum length of the string. • void push_back(char ch): It adds a new character ch at the end of the string. • void pop_back(): It removes a last character of the string. • string& assign(): It assigns new value to the string. • int copy(string& str): It copies the contents of string into another. • char& back(): It returns the reference of last character. • Iterator begin(): It returns the reference of first character. • int capacity(): It returns the allocated space for the string. • const_iterator cbegin(): It points to the first element of the string. • const_iterator cend(): It points to the last element of the string. • void clear(): It removes all the elements from the string. • const_reverse_iterator crbegin(): It points to the last character of the string. • const_char* data(): It copies the characters of string into an array. • bool empty(): It checks whether the string is empty or not. • string& erase(): It removes the characters as specified. • char& front(): It returns a reference of the first character. • string& operator+=(): It appends a new character at the end of the string. • string& operator=(): It assigns a new value to the string. • char operator[](pos): It retrieves a character at specified position pos. • int rfind(): It searches for the last occurrence of the string. • iterator end(): It references the last character of the string. • reverse_iterator rend(): It points to the first character of the string. • void shrink_to_fit(): It reduces the capacity and makes it equal to the size of the string. • char* c_str(): It returns pointer to an array that contains null terminated sequence of characters. • const_reverse_iterator crend(): It references the first character of the string. • reverse_iterator rbegin(): It reference the last character of the string. • void reserve(inr len): It requests a change in capacity. • allocator_type get_allocator();: It returns the allocated object associated with the string.
Non-member Function Overloads
• operator+ Concatenate strings (function ) • relational operators Relational operators for string (function ) • swap Exchanges the values of two strings (function ) • operator>> Extract string from stream (function ) • operator<< Insert string into stream (function ) • getline Get line from stream into string (function )
Operators used for String Objects
• =: assignment • +: concatenation • ==: Equality • !=: Inequality • <: Less than • <=: Less than or equal • >: Greater than • >=: Greater than or equal • []: Subscription • <<: Output • >>: Input
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/* C++ String Library */ /* The C-Style Character String */ // C++ Program to demonstrate the working of getline(), push_back() and pop_back() #include <iostream> #include <string> // for string class using namespace std; // Driver Code int main() { // Declaring string string str; // Taking string input using getline() getline(cin, str); // Displaying string cout << "The initial string is : "; cout << str << endl; // Inserting a character str.push_back('s'); // Displaying string cout << "The string after push_back operation is : "; cout << str << endl; // Deleting a character str.pop_back(); // Displaying string cout << "The string after pop_back operation is : "; cout << str << endl; return 0; }
#include Directive in C++
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }
Assignment Operators in C++
As the name already suggests, these operators help in assigning values to variables. These operators help us in allocating a particular value to the operands. The main simple assignment operator is '='. We have to be sure that both the left and right sides of the operator must have the same data type. We have different levels of operators. Assignment operators are used to assign the value, variable and function to another variable. Assignment operators in C are some of the C Programming Operator, which are useful to assign the values to the declared variables. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=. The following table lists the assignment operators supported by the C language:
=
Simple assignment operator. Assigns values from right side operands to left side operand
+=
Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.
-=
Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.
*=
Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.
/=
Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.
%=
Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.
<<=
Left shift AND assignment operator.
>>=
Right shift AND assignment operator.
&=
Bitwise AND assignment operator.
^=
Bitwise exclusive OR and assignment operator.
|=
Bitwise inclusive OR and assignment operator.
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/* Assignment operators are used to assigning value to a variable. The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. The value on the right side must be of the same data-type of the variable on the left side otherwise the compiler will raise an error. */ // C++ program to demonstrate working of Assignment operators #include <iostream> using namespace std; int main() { // Assigning value 10 to a // using "=" operator int a = 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by adding 10 to a // using "+=" operator a += 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by subtracting 10 from a // using "-=" operator a -= 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by multiplying 10 to a // using "*=" operator a *= 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by dividing 10 from a // using "/=" operator a /= 10; cout << "Value of a is "<<a<<"\n"; return 0; }
length() Function in C++
Return length of string. Returns the length of the string, in terms of bytes. This function is used to find the length of the string in terms of bytes. This is the actual number of bytes that conform the contents of the string , which is not necessarily equal to the storage capacity. This is the number of actual bytes that conform the contents of the string, which is not necessarily equal to its storage capacity. Note that string objects handle bytes without knowledge of the encoding that may eventually be used to encode the characters it contains. Therefore, the value returned may not correspond to the actual number of encoded characters in sequences of multi-byte or variable-length characters (such as UTF-8).
Syntax for length() Function in C++
size_t length() const noexcept;
This function does not accept any parameter. Function returns the number of bytes in the string. size_t is an unsigned integral type (the same as member type string::size_type). Both string::size and string::length are synonyms and return the exact same value. The length() function is also defined inside the string.h header file and works in the same way size() does. Both functions return the same values and are also used in the same way. This function contains single parameter. This function returns the integer value in terms of bytes.
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/* return length of string by length() function code example */ #include<iostream> #include<cstring> using namespace std; main() { string myStr = "This is a sample string"; char myStrChar[] = "This is a sample string"; cout << "String length using string::length() function: " << myStr.length() <<endl; cout << "String length using string::size() function: " << myStr.size() <<endl; cout << "String length using strlen() function for c like string: " << strlen(myStrChar) <<endl; cout << "String length using while loop: "; char *ch = myStrChar; int count = 0; while(*ch != '\0'){ count++; ch++; } cout << count << endl; cout << "String length using for loop: "; count = 0; for(int i = 0; myStrChar[i] != '\0'; i++){ count++; } cout << count; }
strcpy() Function in C++
Copy string. Copies the C string pointed by source into the array pointed by destination, including the terminating null character (and stopping at that point). To avoid overflows, the size of the array pointed by destination shall be long enough to contain the same C string as source (including the terminating null character), and should not overlap in memory with source. strcpy() is a standard library function in C/C++ and is used to copy one string to another. In C it is present in string.h header file and in C++ it is present in cstring header file. It copies the whole string to the destination string. It replaces the whole string instead of appending it. It won't change the source string.
Syntax for strcpy() Function in C++
#include <cstring> char * strcpy ( char * destination, const char * source );
destination
Pointer to the destination array where the content is to be copied.
source
C string to be copied. destination is returned. After copying the source string to the destination string, the strcpy() function returns a pointer to the destination string. • This function copies the entire string to the destination string. It doesn't append the source string to the destination string. In other words, we can say that it replaces the content of destination string by the content of source string. • It does not affect the source string. The source string remains same after copying. • This function only works with C style strings and not C++ style strings i.e. it only works with strings of type char str[]; and not string s1; which are created using standard string data type available in C++ and not C.
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/* copy a character string from source to destination by strcpy() string function code example */ #include <cstring> #include <iostream> using namespace std; int main() { char src[20] = "I am the source."; // large enough to store content of src char dest[30] = "I am the destination."; cout << "dest[] before copy: " << dest << endl; // copy contents of src to dest strcpy(dest,src); cout << "dest[] after copy: " << dest; return 0; }
strlen() Function in C++
Get string length. Returns the length of the C string str. C++ strlen() is an inbuilt function that is used to calculate the length of the string. It is a beneficial method to find the length of the string. The strlen() function is defined under the string.h header file. The strlen() takes a null-terminated byte string str as its argument and returns its length. The length does not include a null character. If there is no null character in the string, the behavior of the function is undefined.
Syntax for strlen() Function in C++
#include <cstring> size_t strlen ( const char * str );
str
a string passed to this function, whose length needs to be found. Here str is the string variable of whose we have to find the length. It takes one parameter which is a pointer that points to the null-terminated byte string. The string is terminated by a null character. If a null character does not terminate it, then the behavior is undefined. It returns an integer giving the length of the passed string. Function returns the length of string. While calculating the total length of a String, the character at the first index is counted as 1 and not 0, i.e. one-based index . The function strlen returns the total number of characters actually present in the char[] and not the total number of character it can hold.
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/* return the length of the C string str by strlen() function code example */ #include <cstring> #include <iostream> using namespace std; int main() { char str1[] = "This a string"; char str2[] = "This is another string"; // find lengths of str1 and str2 // size_t return value converted to int int len1 = strlen(str1); int len2 = strlen(str2); cout << "Length of str1 = " << len1 << endl; cout << "Length of str2 = " << len2 << endl; if (len1 > len2) cout << "str1 is longer than str2"; else if (len1 < len2) cout << "str2 is longer than str1"; else cout << "str1 and str2 are of equal length"; return 0; }
Logical Operators in C++
Logical Operators are used to compare and connect two or more expressions or variables, such that the value of the expression is completely dependent on the original expression or value or variable. We use logical operators to check whether an expression is true or false. If the expression is true, it returns 1 whereas if the expression is false, it returns 0. Assume variable A holds 1 and variable B holds 0:
&&
Called Logical AND operator. If both the operands are non-zero, then condition becomes true. (A && B) is false. The logical AND operator && returns true - if and only if all the operands are true. false - if one or more operands are false.
||
Called Logical OR Operator. If any of the two operands is non-zero, then condition becomes true. (A || B) is true. The logical OR operator || returns true - if one or more of the operands are true. false - if and only if all the operands are false.
!
Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true, then Logical NOT operator will make false. !(A && B) is true. The logical NOT operator ! is a unary operator i.e. it takes only one operand. It returns true when the operand is false, and false when the operand is true.
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/* The operator ! is the C++ operator for the Boolean operation NOT. It has only one operand, to its right, and inverts it, producing false if its operand is true, and true if its operand is false. Basically, it returns the opposite Boolean value of evaluating its operand. The logical operators && and || are used when evaluating two expressions to obtain a single relational result. The operator && corresponds to the Boolean logical operation AND, which yields true if both its operands are true, and false otherwise. */ #include <iostream> using namespace std; main() { int a = 5; int b = 20; int c ; if(a && b) { cout << "Line 1 - Condition is true"<< endl ; } if(a || b) { cout << "Line 2 - Condition is true"<< endl ; } /* Let's change the values of a and b */ a = 0; b = 10; if(a && b) { cout << "Line 3 - Condition is true"<< endl ; } else { cout << "Line 4 - Condition is not true"<< endl ; } if(!(a && b)) { cout << "Line 5 - Condition is true"<< endl ; } return 0; }
getline() Function in C++
Get line from stream into string. The cin is an object which is used to take input from the user but does not allow to take the input in multiple lines. To accept the multiple lines, we use the getline() function. It is a pre-defined function defined in a <string.h> header file used to accept a line or a string from the input stream until the delimiting character is encountered.
Syntax for getline() Function in C++
// (1) istream& getline (istream& is, string& str, char delim); istream& getline (istream&& is, string& str, char delim); // (2) istream& getline (istream& is, string& str); istream& getline (istream&& is, string& str);
is
istream object from which characters are extracted.
str
string object where the extracted line is stored. The contents in the string before the call (if any) are discarded and replaced by the extracted line.
delim
It is the delimiting character. Extracts characters from is and stores them into str until the delimitation character delim is found (or the newline character, '\n', for (2)). The extraction also stops if the end of file is reached in is or if some other error occurs during the input operation. If the delimiter is found, it is extracted and discarded (i.e. it is not stored and the next input operation will begin after it). Note that any content in str before the call is replaced by the newly extracted sequence. Each extracted character is appended to the string as if its member push_back was called. Function returns the same as parameter is. A call to this function may set any of the internal state flags of is if: eofbit: The end of the source of characters is reached during its operations. failbit: The input obtained could not be interpreted as a valid textual representation of an object of this type. In this case, distr preserves the parameters and internal data it had before the call. Notice that some eofbit cases will also set failbit. badbit: An error other than the above happened. (see ios_base::iostate for more info on these) Additionally, in any of these cases, if the appropriate flag has been set with is's member function ios::exceptions, an exception of type ios_base::failure is thrown.
Complexity
Unspecified, but generally linear in the resulting length of str.
Iterator validity
Any iterators, pointers and references related to str may be invalidated.
Data races
Both objects, is and str, are modified.
Exception safety
Basic guarantee: if an exception is thrown, both is and str end up in a valid state.
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/* get line from stream into string by getline() function code example */ // C++ program to demonstrate anomaly of delimitation of getline() function #include <iostream> #include <string> using namespace std; int main() { string name; int id; // Taking id as input cout << "Please enter your id: \n"; cin >> id; // Takes the empty character as input cout << "Please enter your name: \n"; getline(cin, name); // Prints id cout << "Your id : " << id << "\n"; // Prints nothing in name field // as "\n" is considered a valid string cout << "Hello, " << name << " welcome to world !\n"; // Again Taking string as input getline(cin, name); // This actually prints the name cout << "Hello, " << name << " welcome to world !\n"; return 0; }
strcmp() Function in C++
Compare two strings. Compares the C string str1 to the C string str2. This function starts comparing the first character of each string. If they are equal to each other, it continues with the following pairs until the characters differ or until a terminating null-character is reached. This function performs a binary comparison of the characters. For a function that takes into account locale-specific rules, see strcoll. The strcmp() function in C++ compares two null-terminating strings (C-strings). The comparison is done lexicographically. It is defined in the cstring header file.
Syntax for strcmp() Function in C++
int strcmp ( const char * str1, const char * str2 );
str1
pointer to the C-string that needs to be compared.
str2
pointer to the C-string that needs to be compared. Here, str1 stands for left hand side, str2 stands for right hand side. Function returns a positive value if the first differing character in str1 is greater than the corresponding character in str2. Function returns a negative value if the first differing character in str1 is less than the corresponding character in str2. Function returns 0 if str1 and str2 are equal. The strcmp() compares the contents of str1 and str2 lexicographically. The sign of the result is the sign of difference between the first pairs of characters that differ in str1 and str2.
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/* compare two strings by strcmp() string function code example */ #include <cstring> #include <iostream> using namespace std; int main() { char str1[] = "HappyCodings"; char str2[] = "Happy"; // returns -1 because "HappyCodings" < "Happy" lexicographically int result = strcmp(str1, str2); cout << "Comparing " << str1 << " and " << str2 << ": " << result << endl; // returns 1 because "Happy" > "HappyCodings" lexicographically result = strcmp(str2, str1); cout << "Comparing " << str2 << " and " << str1 << ": " << result << endl; // returns 1 because "HappyCodings" = "HappyCodings" lexicographically result = strcmp(str1, str1); cout << "Comparing " << str1 << " and " << str1 << ": " << result; return 0; }
String Library c_str() Function in C++
Get C string equivalent. Returns a pointer to an array that contains a null-terminated sequence of characters (i.e., a C-string) representing the current value of the string object. The basic_string::c_str() is a builtin function in C++ which returns a pointer to an array that contains a null-terminated sequence of characters representing the current value of the basic_string object. This array includes the same sequence of characters that make up the value of the basic_string object plus an additional terminating null-character at the end. This array includes the same sequence of characters that make up the value of the string object plus an additional terminating null-character ('\0') at the end.
Syntax for String c_str() Function in C++
#include <string> const char* c_str() const noexcept;
This function does not accept any parameter. Function returns a pointer to the c-string representation of the string object's value. The pointer returned points to the internal array currently used by the string object to store the characters that conform its value. Both string::data and string::c_str are synonyms and return the same value. The pointer returned may be invalidated by further calls to other member functions that modify the object.
Complexity
Constant
Iterator validity
No changes
Data races
The object is accessed
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* c_str() function returns a pointer to an array that contains a null-terminated sequence of characters (i.e., a C-string) representing the current value of the string object. */ /* Get C string equivalent by c_str() function code example */ #include <bits/stdc++.h> #include <string> using namespace std; int main() { // declare a example string string s1 = "HappyCodings"; // check if the size of the string is same as the // size of character pointer given by c_str if (s1.size() == strlen(s1.c_str())) { cout << "s1.size is equal to strlen(s1.c_str()) " << endl; } else { cout << "s1.size is not equal to strlen(s1.c_str())" << endl; } // print the string printf("%s \n", s1.c_str()); }
Pointers in C++ Language
The pointer in C++ language is a variable, it is also known as locator or indicator that points to an address of a value. In C++, a pointer refers to a variable that holds the address of another variable. Like regular variables, pointers have a data type. For example, a pointer of type integer can hold the address of a variable of type integer. A pointer of character type can hold the address of a variable of character type. You should see a pointer as a symbolic representation of a memory address. With pointers, programs can simulate call-by-reference. They can also create and manipulate dynamic data structures. In C++, a pointer variable refers to a variable pointing to a specific address in a memory pointed by another variable.
Syntax for Pointers in C++
int *ip; // pointer to an integer double *dp; // pointer to a double float *fp; // pointer to a float char *ch // pointer to character
• Pointer reduces the code and improves the performance, it is used to retrieving strings, trees etc. and used with arrays, structures and functions. • We can return multiple values from function using pointer. • It makes you able to access any memory location in the computer's memory. Dynamic memory allocation: In c language, we can dynamically allocate memory using malloc() and calloc() functions where pointer is used. Arrays, Functions and Structures: Pointers in C language are widely used in arrays, functions and structures. It reduces the code and improves the performance. & (ampersand sign): Address operator - Determine the address of a variable. * (asterisk sign): Indirection operator - Access the value of an address. The pointer in C++ language can be declared using * (asterisk symbol).
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/* pointer is a variable in C++ that holds the address of another variable */ #include <iostream> using namespace std; int main () { int var = 20; // actual variable declaration. int *ip; // pointer variable ip = &var; // store address of var in pointer variable cout << "Value of var variable: "; cout << var << endl; // print the address stored in ip pointer variable cout << "Address stored in ip variable: "; cout << ip << endl; // access the value at the address available in pointer cout << "Value of *ip variable: "; cout << *ip << endl; return 0; }
Delete Operator in C++
Deallocate storage space. Default deallocation functions (single-object form). A delete operator is used to deallocate memory space that is dynamically created using the new operator, calloc and malloc() function, etc., at the run time of a program in C++ language. In other words, a delete operator is used to release array and non-array (pointer) objects from the heap, which the new operator dynamically allocates to put variables on heap memory. We can use either the delete operator or delete [ ] operator in our program to delete the deallocated space. A delete operator has a void return type, and hence, it does not return a value.
Syntax for Delete Operator in C++
//ordinary (1) void operator delete (void* ptr) noexcept; //nothrow (2) void operator delete (void* ptr, const std::nothrow_t& nothrow_constant) noexcept; //placement (3) void operator delete (void* ptr, void* voidptr2) noexcept;
ptr
A pointer to the memory block to be released, type-casted to a void*. If this is a null-pointer, the function does nothing. If not null, this pointer value should have been returned by a previous call to operator new, and have not yet been released by a previous call to this function. If the implementation has strict pointer safety, this pointer shall also be a safely-derived pointer.
nothrow_constant
The constant nothrow. This parameter is ignored in the default definition. nothrow_t is the type of constant nothrow.
voidptr2
A void pointer. The value is ignored in the default definition.
size
The first argument passed to the allocation function when the memory block was allocated. std::size_t is an unsigned integral type. This function does not return any value. (1) ordinary delete: Deallocates the memory block pointed by ptr (if not null), releasing the storage space previously allocated to it by a call to operator new and rendering that pointer location invalid. (2) nothrow delete: Same as above (1). The default definition calls the first version (1): ::operator delete(ptr). (3) placement delete: Does nothing. The default allocation and deallocation functions are special components of the standard library; They have the following unique properties: Global: All overloads of operator delete are declared in the global namespace, not within the std namespace. Implicit: The deallocating versions (i.e., all but (3)) are implicitly declared in every translation unit of a C++ program, no matter whether header <new> is included or not. Replaceable: The deallocating versions (i.e., all but (3)) are also replaceable: A program may provide its own definition that replaces the one provided by default or can overload it for specific types. The custom definition shall deallocate the storage referenced by ptr. operator delete is a regular function that can be called explicitly just as any other function. But in C++, delete is an operator with a very specific behavior: An expression with the delete operator, first calls the appropriate destructor (for class types), and then calls a deallocation function. The deallocation function for a class object is a member function named operator delete, if it exists. In all other cases it is a global function operator delete (i.e., this function -- or a more specific overload). If the delete expression is preceded by the scope operator (i.e., ::operator delete), only global deallocation functions are considered. delete expressions that use global deallocation functions always use the signature that takes either a pointer (such as (1)), or a pointer and a size (such as (4)). Preferring always the version with size (4), unless an overload provides a better match for the pointer type. The other signatures ((2) and (3)) are never called by a delete-expression (the delete operator always calls the ordinary version of this function, and exactly once for each of its arguments). These other signatures are only called automatically by a new-expression when their object construction fails (e.g., if the constructor of an object throws while being constructed by a new-expression with nothrow, the matching operator delete function accepting a nothrow argument is called). Non-member deallocation functions shall not be declared in a namespace scope other than the global namespace.
Data races
Modifies the storage referenced by ptr. Calls to allocation and deallocation functions that reuse the same unit of storage shall occur in a single total order where each deallocation happens before the next allocation. This shall also apply to the observable behavior of custom replacements for this function.
Exception safety
No-throw guarantee: this function never throws exceptions. Notice that either an invalid value of ptr, or a value for size that does not match the one passed to the allocation function, causes undefined behavior. Similarly, we can delete the block of allocated memory space using the delete [] operator. delete [ ] pointer_variable; // delete [] ptr; It deallocate for an array.
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/* deallocate storage space by delete operator */ #include <iostream> using namespace std; int main () { // declaration of variables int *ptr1, *ptr2, sum; // allocated memory space using new operator ptr1 = new int; ptr2 = new int; cout << " Enter first number: "; cin >> *ptr1; cout << " Enter second number: "; cin >> *ptr2; sum = *ptr1 + *ptr2; cout << " Sum of pointer variables = " << sum; // delete pointer variables delete ptr1; delete ptr2; return 0; }
this Pointer in C++
Every object in C++ has access to its own address through an important pointer called this pointer. The this pointer is an implicit parameter to all member functions. Therefore, inside a member function, this may be used to refer to the invoking object. Friend functions do not have a this pointer, because friends are not members of a class. Only member functions have a this pointer. In C++ programming, this is a keyword that refers to the current instance of the class. There can be 3 main usage of this keyword in C++: • It can be used to pass current object as a parameter to another method. • It can be used to refer current class instance variable. • It can be used to declare indexers. To understand 'this' pointer, it is important to know how objects look at functions and data members of a class. • Each object gets its own copy of the data member. • All-access the same function definition as present in the code segment. Meaning each object gets its own copy of data members and all objects share a single copy of member functions. Then now question is that if only one copy of each member function exists and is used by multiple objects, how are the proper data members are accessed and updated? The compiler supplies an implicit pointer along with the names of the functions as 'this'. The 'this' pointer is passed as a hidden argument to all nonstatic member function calls and is available as a local variable within the body of all nonstatic functions. 'this' pointer is not available in static member functions as static member functions can be called without any object (with class name). For a class X, the type of this pointer is 'X* '. Also, if a member function of X is declared as const, then the type of this pointer is 'const X *'
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/* The this pointer holds the address of current object, in simple words you can say that this pointer points to the current object of the class. The keyword this identifies a special type of pointer. Suppose that you create an object named x of class A, and class A has a nonstatic member function f(). If you call the function x.f(), the keyword this in the body of f() stores the address of x. You cannot declare the this pointer or make assignments to it. A static member function does not have a this pointer.*/ #include <iostream> using namespace std; class Box { public: // Constructor definition Box(double l = 2.0, double b = 2.0, double h = 2.0) { cout <<"Constructor called." << endl; length = l; breadth = b; height = h; } double Volume() { return length * breadth * height; } int compare(Box box) { return this->Volume() > box.Volume(); } private: double length; // Length of a box double breadth; // Breadth of a box double height; // Height of a box }; int main(void) { Box Box1(3.3, 1.2, 1.5); // Declare box1 Box Box2(8.5, 6.0, 2.0); // Declare box2 if(Box1.compare(Box2)) { cout << "Box2 is smaller than Box1" <<endl; } else { cout << "Box2 is equal to or larger than Box1" <<endl; } return 0; }
If Else Statement in C++
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement,
Syntax for If Statement in C++
if (condition) { // body of if statement }
The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
Syntax for If...Else Statement
if (condition) { // block of code if condition is true } else { // block of code if condition is false }
The if..else statement evaluates the condition inside the parenthesis. If the condition evaluates true, the code inside the body of if is executed, the code inside the body of else is skipped from execution. If the condition evaluates false, the code inside the body of else is executed, the code inside the body of if is skipped from execution. The if...else statement is used to execute a block of code among two alternatives. However, if we need to make a choice between more than two alternatives, we use the if...else if...else statement.
Syntax for If...Else...Else If Statement in C++
if (condition1) { // code block 1 } else if (condition2){ // code block 2 } else { // code block 3 }
• If condition1 evaluates to true, the code block 1 is executed. • If condition1 evaluates to false, then condition2 is evaluated. • If condition2 is true, the code block 2 is executed. • If condition2 is false, the code block 3 is executed. There can be more than one else if statement but only one if and else statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax for If Else If Ladder in C++
if (condition) statement 1; else if (condition) statement 2; . . else statement;
Working of the if-else-if ladder: 1. Control falls into the if block. 2. The flow jumps to Condition 1. 3. Condition is tested. If Condition yields true, goto Step 4. If Condition yields false, goto Step 5. 4. The present block is executed. Goto Step 7. 5. The flow jumps to Condition 2. If Condition yields true, goto step 4. If Condition yields false, goto Step 6. 6. The flow jumps to Condition 3. If Condition yields true, goto step 4. If Condition yields false, execute else block. Goto Step 7. 7. Exits the if-else-if ladder. • The if else ladder statement in C++ programming language is used to check set of conditions in sequence. • This is useful when we want to selectively executes one code block(out of many) based on certain conditions. • It allows us to check for multiple condition expressions and execute different code blocks for more than two conditions. • A condition expression is tested only when all previous if conditions in if-else ladder is false. • If any of the conditional expression evaluates to true, then it will execute the corresponding code block and exits whole if-else ladder.
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/* If Else Statement in C++ Language */ #include <iostream> using namespace std; int main () { // local variable declaration: int a = 100; // check the boolean condition if( a < 20 ) { // if condition is true then print the following cout << "a is less than 20;" << endl; } else { // if condition is false then print the following cout << "a is not less than 20;" << endl; } cout << "value of a is : " << a << endl; return 0; }


Return a pseudorandom int, and change the internal state. Return a "pseudorandom" int, and change the internal state. does not work. Return a "pseudorandom" double in the open
Remove most recently inserted item. Return most recently inserted item. Return, remove most "recently inserted" item. Return true if empty; else false. Return true if 'full' and else
To find the LCM of 2 or more numbers, make "Multiple of Numbers" and Choose Common multiple. Then take lowest common multiple, lowest common multiple is 'LCM' of numbers.
In the C++ Programming, The static keyword allows a variable to maintain its value among different function calls. If the value of a static variable changes when the variable has been