Thread: Problem with Recursion calculing Factorials

Well, I've been learning those things that I didn't knew in theC tutorial of this site, and, in the recursion chapter, there was a homework where you had to write a program which calculates factorials.

This is my function:

Code:

int ObtenerFactorial( int num, int count, int result )

{
	if ( count==num ) return result;
	else
		{
			result *= (num-count);
			ObtenerFactorial( num, count+1, result );
		}
}

I call the function from main this way:

Code:

fflush(stdin);
scanf( "%d", &number );
factorial = ObtenerFactorial( (int)number, 0, 1 );
printf( "\nFactorial de %d: %d\n", number, factorial);

Where 'number' is entered throw the command line.

When the user enter 0, the result is fine, 1. But when you enter any number greater than 0 (1,5,etc), everytimes get out the same result: 1075144832. I don't know what is the problem... I don't expect that you write my homework, just to tell what's wrong: if it's all wrong, I'll write a new program.

You meant return ObtenerFactorial( num, count+1, result );

Thanks for your help, but I don't understand:

FIRST: no, I meant return result;, because if the number is equal to zero, it returns one, and if the count is equal to, for example, 5, in a factorial you don't have "5!=0*1*2*3*4*5", there is no a zero.

SECOND: I really don't understand. That is a part of the main function, if you are refering to the "#include... int main...", if it's not that, I don't know what could be.

Code:

factorial = ObtenerFactorial( (int)number, 0, 1 );

you dont need to type cast it in this. its not need.#

ssharish2005

yeah, later I could see that it's not needed a cast because scanf( "%d", &number) receive only decimals.
I change that line 'ObtenerFact...' for 'return ObtenerFact...', and it works now, thanks you.