C++ For Loop - Learn C++ , C++ Tutorial , C++ programming




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

C++ for Loop Syntax

  • 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.
for(initializationStatement; testExpression; updateStatement) {
    // codes 
}
  • where, only testExpression is mandatory.

How for loop works?

  • The initialization statement is executed only once at the beginning.
  • Then, the test expression is evaluated.
  • If the test expression is false, for loop is terminated. But if the test expression is true, codes inside body of for loop is executed and update expression is updated.
  • 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++

 loop in c++

Example 1: C++ for Loop

// C++ Program to find factorial of a number
// Factorial on n = 1*2*3*...*n

#include <iostream>
using namespace std;

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;
}
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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>
using namespace std;

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;
}


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