A prime number is greater than one and can be divided by one or itself. In other words, prime numbers cannot be divided by anything other than themselves or 1. Prime numbers include 2, 3, 5, 7, 11, 13, 17, 19, 23, etc.

**Program code:**

```
#include <iostream>
using namespace std;
int main() {
int num, i, flag = 0;
printf("Enter a positive integer: ");
cin>>num;
// 0 and 1 are not prime numbers
// change flag to 1 for non-prime number
if (num == 0 || num == 1)
flag = 1;
for (i = 2; i <= num / 2; ++i) {
// if n is divisible by i, then n is not prime
// change flag to 1 for non-prime number
if (num % i == 0) {
flag = 1;
break;
}
}
// flag is 0 for prime numbers
if (flag == 0)
cout<<num<<" is a prime number.";
else
cout<<num<<" is NOT a prime number.";
return 0;
}
```

##### Output:

```
Enter a positive integer: 56
56 is NOT a prime number.
Enter a positive integer: 73
73 is a prime number.
```

*Note: also read about* Diamond Pattern Using Numbers

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Staying up to the mark is what defines me. Hi all! I’m Rabecca Fatima a keen learner, great enthusiast, ready to take new challenges as stepping stones towards flying colors.