# Write a Program in C to Determine Whether a Number is Prime or Not.

“A prime number is one, which is divisible only by 1 or itself.”

To determine whether a number is prime or not, we have to divide the number successively by all numbers from 2 to one less than itself.

If remainder of any of these divisions is zero, the number is not a prime.

If no division yields a zero then the number is a prime number.

### Program in C to Determine Whether a Number is Prime or Not

Steps:
1. Declare integers num and i inside main()
2. Prompt the message allow the input using printf() and scanf()
3. Test whether a Number is prime or not using while() function.

Code:

```#include <stdio.h>

int main()
{

int num, i;

printf("Enter a number");
scanf ("%d",&num);

i=2;

while (i<=num-1)
{

if (num%i==0)
{
printf("Not a prime numbern");
break;
}

i++;
}

if (i==num)

printf("Prime numbern");

return 0;
}
```

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