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 following C++ programming topics:

  • C++ for Loop
  • C++ if, if…else and Nested if…else
  • C++ break and continue Statement
  • C++ Functions
  • Types of User-defined Functions in C++

Example: Check Prime Number

#include <iostream>
using namespace std;

int checkPrimeNumber(int);

int main()
  int n;

  cout << "Enter a positive  integer: ";
  cin >> n;
  if(checkPrimeNumber(n) == 0)
    cout << n << " is a prime number.";
    cout << n << " is not a prime number.";
  return 0;
int checkPrimeNumber(int n)
  bool flag = false;

  for(int i = 2; i <= n/2; ++i)
      if(n%i == 0)
          flag = true;
  return flag;


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.

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

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