This program prints the prime factors of a number. Eg. 56=2x2x2x7 .I've heard its really important and stuff.I believe it is really efficient and simple. Uses two functions : one to check if a number is prime and other to return the next prime number.

#include <stdio.h>
#include <conio.h>

int IsPrime( int );
int FindNextPrime( int );

int main()
{
	int num,divisor = 2;
	printf("Enter number:");
	scanf("%d",&num );
	printf("The prime factors are:\n");

	while( !IsPrime(num))
	{
		while(1)
		{
			if( num%divisor == 0 )
			{
				printf("%d\n",divisor );
				num/=divisor;
				break;
			}
			divisor = FindNextPrime( divisor );
		}
	}
	printf("%d",num);

	getch();
	return 0;
}
	//------ End of main() ------

int IsPrime( int num )		// Checks whether a number is prime
{
	int i;
	for( i=2; i<=num/2; i++ )
	{
		if( num%i == 0 )
			return 0;
	}
	return 1;
}

int FindNextPrime( int num ) // Returns next prime number from passed arg.
{
	do
	{
		if( num == 2 )
			num++;
		else
			num+=2;
	} while( !IsPrime(num));
	return num;
}

errrm... i just have a question: is it possible not to use isprime to search for the prime factors of a number?

To nlsna17: prime figures only get null rest (same as integer result) when divided by themselves and by 1. Let it be N, start dividing N/(N-1), N/(N-2), .. until N/2. If ALL these divisions do not render null rest, it is ALL rests > 0, it is ALL Real results, not a single integer result, then N (Integer as well indeed) is prime.
Sure there are faster ways to find out because I am aware of pundits using large primes to hide/cypher data, but I hope the above definition may help as a starting point.

Bofarull