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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;

bool checkPrimeNumber(int);

int main() {
    int n;

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

    if (checkPrimeNumber(n))
        cout << n << " is a prime number.";
        cout << n << " is not a prime number.";
    return 0;

bool checkPrimeNumber(int n) {
    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;
    return isPrime;


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