A prime number is a positive integer which is divisible only by 1 and itself. Followings are examples of prime numbers: 2, 3, 5, 7, 11, 13,17...
#include <stdio.h>
int main()
{
int n, i, flag = 0;
printf("Enter a positive integer: ");
scanf("%d",&n);
if(n <= 0)
{
printf("Enter positive number only.");
exit(0);
}
for(i=2; i<=n/2; ++i)
{
//checks nonprime number
if(n%i==0)
{
flag=1;
break;
}
}
if (flag==0)
printf("%d is a prime number.",n);
else
printf("%d is not a prime number.",n);
return 0;
}
Output of program
Run-1
Enter a positive integer: 13
13 is a prime number.
Run-2
Enter a positive integer: 10
10 is not a prime number.
Run-3
Enter a positive integer: -5
Enter positive number only.
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