Recursion

[bally28]

Hi freinds,
this is my code for simple recursion program to calculate factorial.
wheneve i return the different value for eg,
1.for return 1, the ans will be 720, which is correct one.
2.for return 0, the ans will be 0.
3.for return 2, the ans will be 1440.

#include<iostream>
using namespace std;


int factorial(int no)
{
if(no==1)
return 1;
//return 0;
//return 2;
else
return (no * factorial(no-1));
}

int main()
{
cout<<"Fatorial is "<<factorial(6);
}

plese help me out..

[ultifinitus]

Well your factorial function is working fine. It doesn't account for negative numbers or 0... but it's fine.

What's your problem? You probably can't go above 13, just because that's about the limit of a 32bit number.

[bally28]

hi,

int factorial(int no)
{
if(no==1)
return 1;
//return 0;
//return 2;

when i remove comment from return 0 or return 2, the ans will be different..

for e.g

int factorial(int no)
{
if(no==1)
//return 1;
return 0;
//return 2;

[D80DSL3A]

when i remove comment from return 0 or return 2, the ans will be different..

That's right, so don't do that. As ultifinitus said, your function is correct. 1 = the correct return value.

[z05DSL3A]

int factorial(int no)
{
    if(no < 0) // Guard against negative numbers
        return 0;  // See edit.
    if(no <=1)  // 0! and 1! = 1
        return 1;
    else
        return (no * factorial(no-1));
}

Edit:
zero is returned to indicate an error! Appropriate error handling code should be used here.

[RisteMK]

This is the right factoriel function:

int factorial(int n)
{
if(n==0) return 1;
return (n * factorial(n-1));
}

[z05DSL3A]

RisteMK,

factorial(-1) --> Boom!

[RisteMK]

yes, i knew that. but when you call the function you will put ' if(n>=0) factorial(n); ' and else print 'put positive number or 0'. then the program will be ok..

[bally28]

thanks guys...
but i want to know why answer is changed when i return different values. thats my question..
once again thanks for help..

[z05DSL3A]

bally28 wrote:

this is my code for simple recursion program to calculate factorial.

bally28 wrote:

but i want to know why answer is changed when i return different values.

It it really your code or have you just copied it from somewhere and do not understand what is going on with it?

[bally28]

Grey Wolf
Hi,
thats my code and i know that how recursion works.
But i just want to know why last value returned is also get multiplied with final answer..
for e.g
return 2;

720*2 = 1440 ?

[z05DSL3A]

The last value returned, as you put it, is actually the first value returned.

If you call factorial(2) it wants to return 2 * factorial(2 - 1), so it calls factorial(2 - 1). As this is 1! it has to return 1 (anything else is wrong*). If you do return 2 to the previous caller that would return 2*2 = 4.

3! = 3 * 2!
    = 3 * 2 * 1!
    = 3 * 2 * 1

* You could call factorial(0) but that would result in a pointless function call and multiplication operation as 0! is also 1.

[bally28]

Hi, Grey Wolf
thanks for ans. My doubt is clear..
Thanks to all for their help..