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# (C++ programming Example for Beginners)

# C++ Program to Check Whether a Number is Prime or Not

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

**Note:** 0 and 1 are not prime numbers.

## Example: Check Prime Number

```
#include <iostream>
using namespace std;
int main(){
int i, n;
bool isPrime = true;
cout << "Enter a positive integer: ";
cin >> n;
// 0 and 1 are not prime numbers
if (n == 0 || n == 1) {
isPrime = false;
}
else {
for (i = 2; i <= n / 2; ++i) {
if (n % i == 0) {
isPrime = false;
break;
}
}
}
if (isPrime)
cout << n << " is a prime number";
else
cout << n << " is not a prime number";
return 0;
}
```

**Output**

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

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

Also, notice that the boolean variable `isPrime` is initialized to `true`

at the beginning of the program.

Since **0** and **1** are not prime numbers, we first check if the input number is one of those numbers or not. If the input number is either **0** or **1**, then the value of `isPrime` is set to `false`

.

Else, the initial value of `isPrime` is left unchanged and the `for`

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

The `for`

loop initiates with an initial value of `i` equals to `2`

and increases the value of `i` by 1 with each iteration.

If the number entered by the user is perfectly divisible by `i`, then `isPrime` is set to `false`

and the number will not be a prime number.

But if the input number is not perfectly divisible by `i` throughout the entirety of the loop, then it means that the input number is only divisible by 1 and that number itself.

So, the given number is a prime number.

## C++ for Beginners: C++ Program to Check Whether a Number is Prime or Not

Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause.The information presented here could also be found in public knowledge domains.