Prime Number Checker

#include <stdio.h>


int main() // prime number checker
{
    int a, b, c;
    int check = 0;

    printf("Enter a positive number to check if it's prime: ");
    scanf("%d", &a);

    if (a == 2 || a == 3)
        check = 1;
    else if (a % 2 == 0)
        check = 0;
    else
    {
        for (b = 2; b <= a / 2; b++)
        {
            if (a % b == 0)
            {
                check = 0;
                b = a / 2;
            }
            else
                check = 1;
        }

    }

    if (check == 1)
        printf("This number is prime.\n");
    else
        printf("This number is not prime.\n");


    return 0;
}