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C++ Programming Code Examples

C++ > Code Snippets Code Examples

String.resize()

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/* String.resize() */ #include <iostream> using std::cout; using std::endl; using std::cin; using std::boolalpha; #include <string> using std::string; void display( const string & ); int main() { string string1; cout << "Statistics before input:\n" << boolalpha; display( string1 ); cout << "\n\nEnter a string: "; cin >> string1; // delimited by whitespace cout << "The string entered was: " << string1; cout << "\nStatistics after input:\n"; display( string1 ); string1.resize( string1.length() + 10 ); cout << "\n\nStats after resizing by (length + 10):\n"; display( string1 ); return 0; } void display( const string &stringRef ) { cout << "capacity: " << stringRef.capacity() << "\nmax size: " << stringRef.max_size() << "\nsize: " << stringRef.size() << "\nlength: " << stringRef.length() << "\nempty: " << stringRef.empty(); } /* Statistics before input: capacity: 0 max size: 1073741820 size: 0 length: 0 empty: true Enter a string: a string The string entered was: a Statistics after input: capacity: 1 max size: 1073741820 size: 1 length: 1 empty: false Stats after resizing by (length + 10): capacity: 11 max size: 1073741820 size: 11 length: 11 empty: false */
String Library empty() Function in C++
Test if string is empty. The C++ string::empty function is used to check whether the string is empty or not. It returns true if the length of the string is zero, else returns false. Returns whether the string is empty (i.e. whether its length is 0). This function does not modify the value of the string in any way. To clear the content of a string, see string::clear.
Syntax for String empty() Function in C++
#include <string> bool empty() const noexcept;
This function does not accept any parameter. empty() function returns true if the string length is 0, false otherwise.
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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/* empty() function checks if the string has no characters, i.e. whether begin() == end(). */ /* check whether the string is empty or not by empty() function code example. */ #include <iostream> #include <string> using namespace std; int main (){ string str1 = "Hello World!."; string str2 = ""; cout<<"String is: "<<str1<<"\n"; cout<<"String length: "<<str1.length()<<"\n"; cout<<"Is it empty?: "<<str1.empty()<<"\n\n"; cout<<"String is: "<<str2<<"\n"; cout<<"String length: "<<str2.length()<<"\n"; cout<<"Is it empty?: "<<str2.empty()<<"\n\n"; return 0; }
String Library capacity() Function in C++
Return size of allocated storage. Returns the size of the storage space currently allocated for the string, expressed in terms of bytes. This function gives the current size of the allocated space for the string. This capacity is not necessarily equal to the string length. It can be equal or greater, with the extra space allowing the object to optimize its operations when new characters are added to the string. Notice that this capacity does not suppose a limit on the length of the string. When this capacity is exhausted and more is needed, it is automatically expanded by the object (reallocating it storage space). The theoretical limit on the length of a string is given by member max_size. The capacity of a string can be altered any time the object is modified, even if this modification implies a reduction in size or if the capacity has not been exhausted (this is in contrast with the guarantees given to capacity in vector containers). The capacity of a string can be explicitly altered by calling member reserve.
Syntax for String capacity() Function in C++
#include <string> size_t capacity() const noexcept;
This function does not accept any parameter. Function returns the size of the storage capacity currently allocated for the string. size_t is an unsigned integral type (the same as member type string::size_type).
Complexity
Unspecified, but generally 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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/* The C++ string::capacity function returns size of currently allocated space to the string, expressed in terms of characters. The returned value is not necessarily equal to the string length. It can be greater than or equal to as compared to the string length, with the extra space required for the string object to optimize its operations. */ /* Return size of allocated storage by string::capacity function code example */ #include <iostream> #include <string> using namespace std; int main (){ string MyString = "Hello World!."; cout<<"The String is: "<<MyString<<"\n"; cout<<"String length: "<<MyString.length()<<"\n"; cout<<"String size: "<<MyString.size()<<"\n"; cout<<"String capacity: "<<MyString.capacity()<<"\n"; return 0; }
Standard Input Stream (cin) in C++
The cin object is used to accept input from the standard input device i.e. keyboard. It is defined in the iostream header file. C++ cin statement is the instance of the class istream and is used to read input from the standard input device which is usually a keyboard. The extraction operator(>>) is used along with the object cin for reading inputs. The extraction operator extracts the data from the object cin which is entered using the keyboard.
Syntax for Standard Input Stream (cin) in C++
cin >> var_name;
>>
is the extraction operator.
var_name
is usually a variable, but can also be an element of containers like arrays, vectors, lists, etc. The "c" in cin refers to "character" and "in" means "input". Hence cin means "character input". The cin object is used along with the extraction operator >> in order to receive a stream of characters. The >> operator can also be used more than once in the same statement to accept multiple inputs. The cin object can also be used with other member functions such as getline(), read(), etc. Some of the commonly used member functions are: • cin.get(char &ch): Reads an input character and stores it in ch. • cin.getline(char *buffer, int length): Reads a stream of characters into the string buffer, It stops when: it has read length-1 characters or when it finds an end-of-line character '\n' or the end of the file eof. • cin.read(char *buffer, int n): Reads n bytes (or until the end of the file) from the stream into the buffer. • cin.ignore(int n): Ignores the next n characters from the input stream. • cin.eof(): Returns a non-zero value if the end of file (eof) is reached. The prototype of cin as defined in the iostream header file is: extern istream cin; The cin object in C++ is an object of class istream. It is associated with the standard C input stream stdin. The cin object is ensured to be initialized during or before the first time an object of type ios_base::Init is constructed. After the cin object is constructed, cin.tie() returns &cout. This means that any formatted input operation on cin forces a call to cout.flush() if any characters are pending for output.
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/* Standard Input Stream (cin) in C++ language */ // cin with Member Functions #include <iostream> using namespace std; int main() { char name[20], address[20]; cout << "Name: "; // use cin with getline() cin.getline(name, 20); cout << "Address: "; cin.getline(address, 20); cout << endl << "You entered " << endl; cout << "Name = " << name << endl; cout << "Address = " << address; return 0; }
String Library resize() Function in C++
Resize string. Resizes the string to a length of n characters. The C++ string::resize function is used to resize the string to a length of specified number of characters (n). If n is smaller than the current string length, the current value is shortened to its first n character, removing the characters beyond the nth. If n is greater than the current string length, the current content is extended by inserting at the end as many characters as needed to reach a size of n. If c is specified, the new elements are initialized as copies of c, otherwise, they are value-initialized characters (null characters).
Syntax for String resize() Function in C++
#include <string> void resize (size_t n); void resize (size_t n, char c);
n
New string length, expressed in number of characters. size_t is an unsigned integral type (the same as member type string::size_type).
c
Character used to fill the new character space added to the string (in case the string is expanded). It does not return any value.
Complexity
Unspecified, but generally up to linear in the new string length.
Iterator validity
Any iterators, pointers and references related to this object may be invalidated.
Data races
The object is modified.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the string. If n is greater than max_size, a length_error exception is thrown. A bad_alloc exception is thrown if the function needs to allocate storage and fails.
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/* The C++ string::resize function is used to resize the string to a length of specified number of characters (n). If n is less than the current string length then the content is reduced to the first n characters of the string. If n is greater than the current string length, then the new characters are inserted at the end of the string. If c is specified, then new characters are initialized with c, else they are value-initialized. */ /* resize the string to the length of k characters by string::resize function code example. */ #include <iostream> #include <string> using namespace std; int main (){ string MyString = "Learn Python"; //size of the string is reduced to 6 MyString.resize(6); //size of the string is expanded to 7 with character 'C' MyString.resize(7, 'C'); //size of the string is expanded to 9 with character '+' MyString.resize(9, '+'); cout<<"MyString contains: "<<MyString; return 0; }
main() Function in C++
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
String Library size() Function in C++
Return length of string. Returns the length of the string, in terms of bytes. 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). Both string::size and string::length are synonyms and return the same value.
Syntax for String size() Function in C++
#include <string> size_t size() 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).
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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/* return the length of the string in terms of bytes by string size() function code example. */ #include <iostream> #include <string> using namespace std; int main() { string s1("Quick! from book www.com."); string s2("Lord test "); string s3("Don't test"); s1.erase(0, 7); s1.replace(9, 5, s2); s1.replace(0, 1, "s"); s1.insert(0, s3); s1.erase(s1.size()-1, 1); s1.append(3, '!'); int x = s1.find(' '); //find a space while( x < s1.size() ) //loop while spaces remain { s1.replace(x, 1, "/"); //replace with slash x = s1.find(' '); //find next space } cout << "s1: " << s1 << endl; 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; }
#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; }
String Library max_size() Function in C++
Return maximum size of string. Returns the maximum length the string can reach. The C++ string::max_size function returns the maximum length the string can reach. The function returns the maximum potential length the string can reach due to known system or library implementation limitations. This is the maximum potential length the string can reach due to known system or library implementation limitations, but the object is not guaranteed to be able to reach that length: it can still fail to allocate storage at any point before that length is reached.
Syntax for String max_size() Function in C++
#include <string> size_t max_size() const noexcept;
It does not contain any parameter. Function returns the maximum length the string can reach. size_t is an unsigned integral type (the same as member type string::size_type).
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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/* max_size() function returns the maximum length the string can reach due to known system. */ /* Return maximum size of string by max_size function code example */ // comparing size, length, capacity and max_size #include <iostream> #include <string> int main () { std::string str ("Test string"); std::cout << "size: " << str.size() << "\n"; std::cout << "length: " << str.length() << "\n"; std::cout << "capacity: " << str.capacity() << "\n"; std::cout << "max_size: " << str.max_size() << "\n"; 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; }


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To check whether the input alphabet is vowel or not a vowel in C++, Enter a Character, then check the character for Vowel. The character is vowel, only if it's equal to a, A, e, E, i, I, o, O
Basically it implements on a big network. The time complexity of this algorithm is O(log(n)). This algorithm takes the input of the number of edges 'e'. It connects vertexes randomly &