**Example to check whether an integer (entered by the user) is a prime number or not using for loop and if…else statement.**

**Example to check whether an integer (entered by the user) is a prime number or not using for loop and if…else statement.**

To understand this example, you should have the knowledge of following C++ programming topics:

- if, if…else and Nested if…else
- for Loop
- break and continue Statement

A positive integer which is only divisible by 1 and itself is known as prime number.

For example: 13 is a prime number because it is only divisible by 1 and 13 but, 15 is not prime number because it is divisible by 1, 3, 5 and 15.

## Example: Check Prime Number

#include <iostream> using namespace std; int main() { int n, i; bool isPrime = true; cout << "Enter a positive integer: "; cin >> n; for(i = 2; i <= n / 2; ++i) { if(n % i == 0) { isPrime = false; break; } } if (isPrime) cout << "This is a prime number"; else cout << "This is not a prime number"; return 0; }

**Output**

Enter a positive integer: 29 This is a prime number.

This program takes a positive integer from user and stores it in variable `n`.

Then, `for`

loop is executed which checks whether the number entered by user is perfectly divisible by `i` or not.

The foor loop initiates with an initial value of `i` equals to 2 and increasing the value of `i` in each iteration.

If the number entered by user is perfectly divisible by `i` then, *isPrime* is set to `false` and the number will not be a prime number.

But, if the number is not perfectly divisible by `i` until test condition `i <= n/2`

is true means, it is only divisible by 1 and that number itself.

So, the given number is a prime number.