Thread: Recursion

I'm having trouble understanding the following code fragment. Should it return 3 * 3=9

Code:

#include <stdio.h>
int factorial(int num);
void main()
{
    int fact, num=3;
    fact = factorial(num);
    printf("%d factorial = %d\n", num, fact);
}

int factorial(int num)
{
    /* num factorial. Assumes num >= 1 */
    if (num == 1) return 1;
    else return (num * factorial(num-1));
}

i still don't understand it, i tried the iterated version:

Code:

#include <stdio.h>
int factorial(int num);
void main()
{
    int fact, num=4;
    fact = factorial(num);
    printf("%d factorial = %d\n", num, fact);
}

int factorial(int num)
{
    /* num factorial. Assumes num >= 1 */
    int i, fact=1;
    for (i=2; i<=num; i++)
    {
        fact *= i;
        printf("\n%d\n", i);
    }
    printf("\n");
    return fact;
}

but it doesn't add up:

i = 2

i = 3

i = 4

4 factorial = 24

2*1(fact) = 2
3*1(fact) = 5
4*1(fact) = 10



hmm?:|

Yeah 1*2*3*4 = 24. I just don't get what fact *= i;
does.
To me it reads

1*1= 1

2*1 = 3 (incremented from previous value)

3*1 = 6 (incremented from previous value)

4 * 4 = 22 (incremented from previous value)

why is it not 24?:|

Quantum,

i=2 fact*2
i=3 fact*3
i=4 fact*4

gives me 16.

fact *= i; means to multiply fact by i and store the result in fact.

thanks guys, the *= expression confused me a bit, and the recursion bit made it even more confusing since i didn't understand the iterated version.

> void main()
And 200+ posts - tsk

The theory is that if you've made 200 posts to this site, the chances are you've posted a program before, and if you used void main, you'd have been told off, and learned to not do it again.

nope, i don't believe i've used void main anywhere. Like i said it was specifically with this example. Thanks for your help everyone.