Determining if a number is prime

Question

I have perused a lot of code on this topic, but most of them produce the numbers that are prime all the way up to the input number. However, I need code which only checks w

Answer 1

#define TRUE 1
#define FALSE -1

int main()
{
/* Local variables declaration */
int num = 0;
int result = 0;

/* Getting number from user for which max prime quadruplet value is 
to be found */
printf("\nEnter the number :");
scanf("%d", &num);

result = Is_Prime( num );

/* Printing the result to standard output */
if (TRUE == result)
    printf("\n%d is a prime number\n", num);
else
    printf("\n%d is not a prime number\n", num);

return 0;
}

int Is_Prime( int num )
{
int i = 0;

/* Checking whether number is negative. If num is negative, making
it positive */
if( 0 > num )
    num = -num;

/* Checking whether number is less than 2 */
if( 2 > num )
    return FALSE;

/* Checking if number is 2 */
if( 2 == num )
    return TRUE;

/* Checking whether number is even. Even numbers
are not prime numbers */
if( 0 == ( num % 2 ))
    return FALSE;

/* Checking whether the number is divisible by a smaller number
1 += 2, is done to skip checking divisibility by even numbers.
Iteration reduced to half */
for( i = 3; i < num; i += 2 )
    if( 0 == ( num % i ))
        /* Number is divisible by some smaller number, 
        hence not a prime number */
        return FALSE;

return TRUE;
}