problem with my prime number program

well this program was made so it could tell u the if the number entered is a prime number or not...but i aint workin'

Code:

`#include <stdio.h>`

int prime_number ( int );

int main()

{

int num1, sum;

printf ("Enter a number:");

scanf ("%d", &num1 );

sum = prime_number ( num1 );

if ( sum == 1){

printf ("%d is not a prime number", num1 );

else

if ( sum == 0 )

printf ("%d is a prime number", num1)

return 0;

}

int prime_number ( int a)

{

int num2, tot;

num2 = a/2;

tot = a/num2;

if ( tot == 2 )

return 1;

else

return 0;

}