# C++ Program to Check Prime Number By Creating a Function

You will learn to check whether a number entered by the user is prime or not by passing it to a user-defined function.

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

## Example: Check Prime Number

``````#include <iostream>
using namespace std;

int main() {
int n;

cout << "Enter a positive  integer: ";
cin >> n;

cout << n << " is a prime number.";
else
cout << n << " is not a prime number.";
return 0;
}

bool isPrime = true;

// 0 and 1 are not prime numbers
if (n == 0 || n == 1) {
isPrime = false;
}
else {
for (int i = 2; i <= n / 2; ++i) {
if (n % i == 0) {
isPrime = false;
break;
}
}
}
return isPrime;
}
```
```

Output

```Enter a positive  integer: 23
23 is a prime number.```

In this example, the number entered by the user is passed to the `checkPrimeNumber()` function.

This function returns `true` if the number passed to the function is a prime number, and returns `false` if the number passed is not a prime number.

The detailed logic of the `checkPrimeNumber()` function is given in our C++ Prime Number tutorial.

Finally, the appropriate message is printed from the `main()` function