1. Ok, in C anything nonzero evaluates to true, conversely 0 evaluates to false. So you could:
Code:
```int main (void){

int num;

printf("Enter a Number to Test if it is Prime: ");
scanf("%d",&num);

if(is_prime(num))
printf("%d is prime", num);
else
printf("%d is not prime", num);

system("PAUSE");
return(0);
} /* End of Main*/```

2. Note that N is unused and you are calling is_prime twice for no good reason...
Code:
```  Y = is_prime (num);
N = is_prime (num);

if (Y == 1)
{
printf("%d is a Prime Number\n", num);
}
else
{
printf("%d is NOT a Prime Number\n", num);
}```
You could have also done this...
Code:
```if (is_prime ( num ))
printf("%d is a prime number.\n\n", num);
else
printf("%d is not a prime number.\n\n",num);```
or maybe this...
Code:
```printf ("%d is ",num);
if (!is_prime (num))
printf("not ");
printf("a prime number\n\n");```

In your is_prime function you could have done this...
Code:
```int is_prime (int p_num)
{ int i;

if ( ! (p_num & 1) )   // prime numbers are all odd numbers
return 0;

for(i = 3; i < p_num; i ++)  // no need to check 1 or 2
if (p_num%i==0)
return 0;
return 1; }```

There are always other ways of doing things...