A Program to Check a Prime Number

In this example, we are giving a program to check whether a number is prime or not. A number can be said prime if the number is divisible only by 1 and itself. For example: 2, 3, 5, 7, 11, 13, 17, 19 etc.

Program to check prime:

  1. #include <iostream>
  2. using namespace std;
  3. int main() {
  4.     int n, i, flag = 0;
  5.     cout << "Enter a positive integer: ";
  6.     cin >> n;
  8.     for (i = 2; i < n / 2; ++i) {
  10.         // condition for non prime number
  11.         if (n % i == 0) {
  12.             flag = 1;
  13.             break;
  14.         }
  15.     }
  17.     if (n == 1) {
  18.         cout << "1 is neither prime nor composite.";
  19.     }
  20.     else {
  21.         if (flag == 0)
  22.             cout << n << "is a prime number.";
  23.         else
  24.             cout << n << "is not a prime number.";
  25.     }
  27.     return 0;
  28. }

Output:

Enter a positive integer: 7
7 is a prime number.

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