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C++ Programming Code Examples

C++ > Code Snippets Code Examples

Taking the sum of values from a stream

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/* Taking the sum of values from a stream */ #include <iostream> #include <iterator> using std::cout; using std::endl; using std::cin; using std::istream_iterator; template <typename Iter> double mySum (Iter begin, Iter end) { double sum = 0.0; for( ; begin != end ;) sum += *begin++; return sum; } int main() { cout << "Ctrl-Z to stop" << endl; double av = mySum(istream_iterator<double>(cin), istream_iterator<double>()); cout << "The sum value is " << av << endl; return 0; } /* Ctrl-Z to stop ^Z The sum value is 0 */
Return Statement in C++
A return statement ends the processing of the current function and returns control to the caller of the function. A value-returning function should include a return statement, containing an expression. If an expression is not given on a return statement in a function declared with a non-void return type, the compiler issues an error message. If the data type of the expression is different from the function return type, conversion of the return value takes place as if the value of the expression were assigned to an object with the same function return type.
Syntax for Return Statement in C++
return[expression];
For a function of return type void, a return statement is not strictly necessary. If the end of such a function is reached without encountering a return statement, control is passed to the caller as if a return statement without an expression were encountered. In other words, an implicit return takes place upon completion of the final statement, and control automatically returns to the calling function. If a return statement is used, it must not contain an expression. The following are examples of return statements:
return; /* Returns no value */ return result; /* Returns the value of result */ return 1; /* Returns the value 1 */ return (x * x); /* Returns the value of x * x */
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/* illustrate Methods returning a value using return statement in C++ code example */ #include <iostream> using namespace std; // non-void return type // function to calculate sum int SUM(int a, int b) { int s1 = a + b; // method using the return // statement to return a value return s1; } // Driver method int main() { int num1 = 10; int num2 = 10; int sum_of = SUM(num1, num2); cout << "The sum is " << sum_of; return 0; }
Relational Operators in C++
A relational operator is used to check the relationship between two operands. C++ Relational Operators are used to relate or compare given operands. Relational operations are like checking if two operands are equal or not equal, greater or lesser, etc. Relational Operators are also called Comparison Operators. • == Is Equal To 4 == 9 gives us false • != Not Equal To 4 != 9 gives us true • > Greater Than 4 > 9 gives us false • < Less Than 4 < 9 gives us true • >= Greater Than or Equal To 4 >= 9 give us false • <= Less Than or Equal To 4 <= 9 gives us true
==
Equal To Operator (==) is used to compare both operands and returns 1 if both are equal or the same, and 0 represents the operands that are not equal. The equal to == operator returns true - if both the operands are equal or the same false - if the operands are unequal int x = 10; int y = 15; int z = 10; x == y // false x == z // true The relational operator == is not the same as the assignment operator =. The assignment operator = assigns a value to a variable, constant, array, or vector. It does not compare two operands.
!=
Not Equal To Operator (!=) is the opposite of the Equal To Operator and is represented as the (!=) operator. The Not Equal To Operator compares two operands and returns 1 if both operands are not the same; otherwise, it returns 0. The not equal to != operator returns true - if both operands are unequal false - if both operands are equal. int x = 10; int y = 15; int z = 10; x != y // true x != z // false
>
Greater than Operator (>) checks the value of the left operand is greater than the right operand, and if the statement is true, the operator is said to be the Greater Than Operator. The greater than > operator returns true - if the left operand is greater than the right false - if the left operand is less than the right int x = 10; int y = 15; x > y // false y > x // true
<
Less than Operator (<) is used to check whether the value of the left operand is less than the right operand, and if the statement is true, the operator is known as the Less than Operator. The less than operator < returns true - if the left operand is less than the right false - if the left operand is greater than right int x = 10; int y = 15; x < y // true y < x // false
>=
Greater than Equal To Operator (>=) checks whether the left operand's value is greater than or equal to the right operand. If the statement is true, the operator is said to be the Greater than Equal to Operator. The greater than or equal to >= operator returns true - if the left operand is either greater than or equal to the right false - if the left operand is less than the right int x = 10; int y = 15; int z = 10; x >= y // false y >= x // true z >= x // true
<=
Less than Equal To Operator (<=) checks whether the value of the left operand is less than or equal to the right operand, and if the statement is true, the operator is said to be the Less than Equal To Operator. The less than or equal to operator <= returns true - if the left operand is either less than or equal to the right false - if the left operand is greater than right int x = 10; int y = 15; x > y // false y > x // true
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/* Relational Operators are used for the comparison of the values of two operands. For example, checking if one operand is equal to the other operand or not, an operand is greater than the other operand or not, etc. Some of the relational operators are (==, >= , <= ). */ #include <iostream> using namespace std; main() { int a = 21; int b = 10; int c ; if( a == b ) { cout << "Line 1 - a is equal to b" << endl ; } else { cout << "Line 1 - a is not equal to b" << endl ; } if( a < b ) { cout << "Line 2 - a is less than b" << endl ; } else { cout << "Line 2 - a is not less than b" << endl ; } if( a > b ) { cout << "Line 3 - a is greater than b" << endl ; } else { cout << "Line 3 - a is not greater than b" << endl ; } /* Let's change the values of a and b */ a = 5; b = 20; if( a <= b ) { cout << "Line 4 - a is either less than \ or equal to b" << endl ; } if( b >= a ) { cout << "Line 5 - b is either greater than \ or equal to b" << 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; }
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; }
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; }
Iterator Library istream_iterator in C++
Istream iterators are input iterators that read successive elements from an input stream (such as cin). std::istream_iterator is a single-pass input iterator that reads successive objects of type T from the std::basic_istream object for which it was constructed, by calling the appropriate operator>>. The actual read operation is performed when the iterator is incremented, not when it is dereferenced. The first object is read when the iterator is constructed. Dereferencing only returns a copy of the most recently read object. They are constructed from a basic_istream object, to which they become associated, so that whenever operator++ is used on the iterator, it extracts an element from the stream (using operator>>). This kind of iterator has a special state as an end-of-stream iterator, which is acquired if an input operations fails (as returned by fail after an operation with the associated stream), and is also the resulting value of a default-constructed object.
Syntax for istream_iterator in C++
#include <iterator> template <class T, class charT=char, class traits=char_traits<charT>, class Distance = ptrdiff_t> class istream_iterator;
T
Element type for the iterator: The type of elements extracted from the stream
charT
First template parameter of the associated basic_istream object: The type of elements the stream handles (char for istream).
traits
Second template parameter of the associated basic_istream: Character traits for the elements the stream handles.
Distance
Type to represent the difference between two iterators (generally a signed integral type, such as ptrdiff_t). The default template arguments correspond to an instantiation that uses an istream object as associated stream.
Member types
member definition in istream_iterator description istream_type basic_istream<charT,traits> Type of the associated input stream iterator_category input_iterator_tag Input iterator value_type T Type of the elements pointed by the iterator char_type charT Type of the characters handled by the associated stream traits_type traits Character traits for associated stream difference_type Distance Distance type pointer const T* reference const T&
Member functions
• (constructor) Construct istream iterator (public member function ) • operator* Dereference iterator (public member function ) • operator-> Dereference iterator (public member function ) • operator++ Increment iterator position (public member function )
Non-member function overloads
• relational operators Relational operators for istream_iterator (function template )
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/* istream_iterator is a special input iterator that read successive elements from an input stream. */ // Cpp program code example to illustrate // Read a bunch of strings from a file sort them lexicographically and print them to output stream #include <algorithm> #include <fstream> #include <iostream> #include <iterator> #include <string> #include <vector> using namespace std; int main() { // Define a vector to store the strings received from input vector<string> strings_v; // Define the filestream object used to read data from file ifstream fin("input_file.txt"); // Get input stream and end of stream iterators istream_iterator<string> fin_it(fin); istream_iterator<string> eos; // Get output stream iterators ostream_iterator<string> cout_it(cout, " "); // Copy elements from input to vector using copy function copy(fin_it, eos, back_inserter(strings_v)); // Sort the vector sort(strings_v.begin(), strings_v.end()); // Copy elements from vector to output copy(strings_v.begin(), strings_v.end(), cout_it); return 0; }
Iterators in C++ Language
Iterators are just like pointers used to access the container elements. Iterators are one of the four pillars of the Standard Template Library or STL in C++. An iterator is used to point to the memory address of the STL container classes. For better understanding, you can relate them with a pointer, to some extent. Iterators act as a bridge that connects algorithms to STL containers and allows the modifications of the data present inside the container. They allow you to iterate over the container, access and assign the values, and run different operators over them, to get the desired result.
Syntax for Iterators in C++
<ContainerType> :: iterator; <ContainerType> :: const_iterator;
• Iterators are used to traverse from one element to another element, a process is known as iterating through the container. • The main advantage of an iterator is to provide a common interface for all the containers type. • Iterators make the algorithm independent of the type of the container used. • Iterators provide a generic approach to navigate through the elements of a container. Operator (*) : The '*' operator returns the element of the current position pointed by the iterator. Operator (++) : The '++' operator increments the iterator by one. Therefore, an iterator points to the next element of the container. Operator (==) and Operator (!=) : Both these operators determine whether the two iterators point to the same position or not. Operator (=) : The '=' operator assigns the iterator. Iterators can be smart pointers which allow to iterate over the complex data structures. A Container provides its iterator type. Therefore, we can say that the iterators have the common interface with different container type. The container classes provide two basic member functions that allow to iterate or move through the elements of a container: begin(): The begin() function returns an iterator pointing to the first element of the container. end(): The end() function returns an iterator pointing to the past-the-last element of the container. Input Iterator: An input iterator is an iterator used to access the elements from the container, but it does not modify the value of a container. Operators used for an input iterator are: Increment operator(++), Equal operator(==), Not equal operator(!=), Dereference operator(*). Output Iterator: An output iterator is an iterator used to modify the value of a container, but it does not read the value from a container. Therefore, we can say that an output iterator is a write-only iterator. Operators used for an output iterator are: Increment operator(++), Assignment operator(=). Forward Iterator: A forward iterator is an iterator used to read and write to a container. It is a multi-pass iterator. Operators used for a Forward iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=). Bidirectional iterator: A bidirectional iterator is an iterator supports all the features of a forward iterator plus it adds one more feature, i.e., decrement operator(--). We can move backward by decrementing an iterator. Operators used for a Bidirectional iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=), Decrement operator(--). Random Access Iterator: A Random Access iterator is an iterator provides random access of an element at an arbitrary location. It has all the features of a bidirectional iterator plus it adds one more feature, i.e., pointer addition and pointer subtraction to provide random access to an element. Following are the disadvantages of an iterator: • If we want to move from one data structure to another at the same time, iterators won't work. • If we want to update the structure which is being iterated, an iterator won?t allow us to do because of the way it stores the position. • If we want to backtrack while processing through a list, the iterator will not work in this case. Following are the advantages of an iterator: • Ease in programming: It is convenient to use iterators rather than using a subscript operator[] to access the elements of a container. If we use subscript operator[] to access the elements, then we need to keep the track of the number of elements added at the runtime, but this would not happen in the case of an iterator. • Code Reusability: A code can be reused if we use iterators. In the above example, if we replace vector with the list, and then the subscript operator[] would not work to access the elements as the list does not support the random access. However, we use iterators to access the elements, then we can also access the list elements. • Dynamic Processing: C++ iterators provide the facility to add or delete the data dynamically.
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/* Iterators in C++ language */ // C++ code to demonstrate the working of next() and prev() #include<iostream> #include<iterator> // for iterators #include<vector> // for vectors using namespace std; int main() { vector<int> ar = { 1, 2, 3, 4, 5 }; // Declaring iterators to a vector vector<int>::iterator ptr = ar.begin(); vector<int>::iterator ftr = ar.end(); // Using next() to return new iterator // points to 4 auto it = next(ptr, 3); // Using prev() to return new iterator // points to 3 auto it1 = prev(ftr, 3); // Displaying iterator position cout << "The position of new iterator using next() is : "; cout << *it << " "; cout << endl; // Displaying iterator position cout << "The position of new iterator using prev() is : "; cout << *it1 << " "; cout << endl; return 0; }
For Loop Statement in C++
In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
Syntax of For Loop Statement in C++
for (initialization; condition; update) { // body of-loop }
initialization
initializes variables and is executed only once.
condition
if true, the body of for loop is executed, if false, the for loop is terminated.
update
updates the value of initialized variables and again checks the condition. A new range-based for loop was introduced to work with collections such as arrays and vectors.
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/* For Loop Statement in C++ Language */ // C++ program to find the sum of first n natural numbers // positive integers such as 1,2,3,...n are known as natural numbers #include <iostream> using namespace std; int main() { int num, sum; sum = 0; cout << "Enter a positive integer: "; cin >> num; for (int i = 1; i <= num; ++i) { sum += i; } cout << "Sum = " << sum << endl; return 0; }
Standard Output Stream (cout) in C++
The cout is a predefined object of ostream class. It is connected with the standard output device, which is usually a display screen. The cout is used in conjunction with stream insertion operator (<<) to display the output on a console. On most program environments, the standard output by default is the screen, and the C++ stream object defined to access it is cout.
Syntax for cout in C++
cout << var_name; //or cout << "Some String";
The syntax of the cout object in C++: cout << var_name; Or cout << "Some String";
<<
is the insertion operator
var_name
is usually a variable, but can also be an array element or elements of containers like vectors, lists, maps, etc. The "c" in cout refers to "character" and "out" means "output". Hence cout means "character output". The cout object is used along with the insertion operator << in order to display a stream of characters. The << operator can be used more than once with a combination of variables, strings, and manipulators. cout is used for displaying data on the screen. The operator << called as insertion operator or put to operator. The Insertion operator can be overloaded. Insertion operator is similar to the printf() operation in C. cout is the object of ostream class. Data flow direction is from variable to output device. Multiple outputs can be displayed using cout.
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/* standard output stream (cout) in C++ language */ #include <iostream> using namespace std; int main() { string str = "Do not interrupt me"; char ch = 'm'; // use cout with write() cout.write(str,6); cout << endl; // use cout with put() cout.put(ch); return 0; }


"Constructor" is automatically called when an object create. It is "special member function" of the class. Variable declaration, constructor without argument, and which constructor has