For Loops in C++

Loops are used in programming to repeat a specific block of code. In this tutorial, you will learn to create a for loop in C++ programming (with examples).

• Loops are used in programming to repeat a specific block until some end condition is met. There are three type of loops in C++ programming:

1. for loop
2. while loop
3. do...while loop

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C++ for Loop Syntax

for(initializationStatement; testExpression; updateStatement) 

{

// codes 

}

where, only testExpression is mandatory.

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How for loop works?

1. The initialization statement is executed only once at the beginning.
2. Then, the test expression is evaluated.
3. If the expression of the check is incorrect, it is terminated for loop. Moreover, if the check expression is correct, codes are executed within the body of for loop and update expression is changed.
4. Again, the test expression is evaluated and this process repeats until the test expression is false.

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Flowchart of for Loop in C++

For loop in C++

// C++ Program to find factorial of a number

// Factorial on n = 1*2*3*...*n

#include <iostream.h>

int main() 

{

    int i, n, factorial = 1;

    cout << "Enter a positive integer: ";

    cin >> n;

    for (i = 1; i <= n; ++i) {

        factorial *= i;   // factorial = factorial * i;

    }

    cout<< "Factorial of "<<n<<" = "<<factorial;

    return 0;

}

Output

Enter a positive integer: 5

Factorial of 5 = 120

• In the program, user is asked to enter a positive integer which is stored in variable n(suppose user entered 5). Here is the working of for loop:

1. Initially, i is equal to 1, test expression is true, factorial becomes 1.
2. i is updated to 2, test expression is true, factorial becomes 2.
3. i is updated to 3, test expression is true, factorial becomes 6.
4. i is updated to 4, test expression is true, factorial becomes 24.
5. i is updated to 5, test expression is true, factorial becomes 120.
6. i is updated to 6, test expression is false, for loop is terminated.

• In the above program, variable i is not used outside of the for loop. In such cases, it is better to declare the variable in for loop (at initialization statement).

#include <iostream.h>

int main() 

{

 int n, factorial = 1;

cout << "Enter a positive integer: ";

cin >> n;

for (int i = 1; i <= n; ++i) {

factorial *= i;   // factorial = factorial * i;

}

cout<< "Factorial of "<<n<<" = "<<factorial;

return 0;

}