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

In this C++ programming example, we will learn about the prime number program in C++. We specifically write a program to check the entered number is prime or not. Let us start by understanding what is a prime number.

Prime Number:

A Prime Number is a number that is only divisible by 1 and itself. Example: 2, 3, 5, 7, 11, 13, 17, etc. These numbers are only divisible by 1 and the number itself.

Note:
0 and 1 is not a prime number and 2 is the only even and smallest prime number.

To understand the following program, you should have a basic idea about the following topics in C++ programming.

• C++ if…else statement
• C++ for Loop
• C++ break Statement

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Check Prime Number in C++

The program takes a user input for a number that needed to be checked for prime number. Since 0 and 1 are not prime numbers so we first check them using the if statement. And if the number is other than 0 and 1 the execution control goes to the else part of the statement.

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

#include <iostream>
using namespace std;

int main()
{
  int i, num, flag;

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

  // checking for 0 and 1
  if (num == 0 || num == 1)
  {
    flag = 1;
  }
  else
  {
    for (i = 2; i <= num / 2; ++i)
    {
      if (num % i == 0)
      {
        flag = 1;
        break;
      }
    }
  }

  if (flag == 0)
    cout << num << " is a prime number";
  else
    cout << num << " is NOT a prime number";

  return 0;
}

Output:

Enter a positive integer: 13
13 is a prime number

You may go through the following program of prime numbers in C++.

• C++ Program to Print Prime numbers in a Given Range

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