1.      Program to check whether a number is prime.

1. #include <iostream.h>

2. #include <conio.h>

3. int main() {

4.     int n, i, isPrime = 1;

5.     cout << "Enter a positive integer: ";

6.     cin >> n;

7.     // 0 and 1 are not prime numbers

8.     if (n == 0 || n == 1) {

9.         isPrime = 0;

10.     } else {

11.         for (i = 2; i <= n/2; ++i) {

12.             if (n % i == 0) {

13.                 isPrime = 0;

14.                 break;

15.             }

16.         }

17.     }

18.     if (isPrime)

19.                 cout << n << " is a prime number.\n";

20.     else

21.                 cout << n << " is not a prime number.\n";

22.     getch();

23.     return 0;

25. }