recursive factorial

[tNK]

Hello everyone so I'm trying to understand this code.

I'm throwing 5 into the paramter aka int x, and the function starts
5 * 4 = 20
20 * 3 = 60
60 * 2 = 120

now x is finally 1 which is == to the base case and it returns the total number we calculated after the else statement.

Am I understanding this correctly or is there a better way to understand this. Thank you in advance for your help.

  #include <iostream>
using namespace std;

int factorialFinder(int x){
    if(x==1){ 
    return 1;
    }else{
        return x*factorialFinder(x-1);
    }
}

int main()
{
    cout << factorialFinder(5) << endl;
}

[48T7M4Gy]

Sounds reasonable, and it works too! :)

[JLBorges]

> I'm throwing 5 into the paramter aka int x, and the function starts
> 5 * 4 = 20
> 20 * 3 = 60
> 60 * 2 = 120

It is the other way around.

factorial(5) == 5 * factorial(4) == 5 * 24 == 120
ie. factorial(5) == 5 * factorial(4) == 5 * ( 4 * factorial(3) ) == 5 * ( 4 * 6 ) == 5 * 24 == 120
etc.

#include <iostream>
#include <string>

int factorial( int n )
{
    static int depth = 0 ;

    ++depth ;
    const std::string tab( depth*4, ' ' ) ;
    std::cout << tab <<  depth << ". factorial(" << n << ") == " ;

    if( n < 2 )
    {
        std::cout << 1 << '\n' ;
        --depth ;
        return 1 ;
    }
    else
    {
        std::cout << n << " * factorial(" << n-1 << ")\n" ;
        const int fact_nm1 = factorial(n-1) ;
        const int result = n * fact_nm1 ;
        std::cout << tab << depth << ". factorial(" << n << ") == "
                  << n << " * " << fact_nm1 << " == " << result << '\n' ;
        --depth ;
        return result ;
    }
}

int main()
{
    factorial(8) ;
}

    1. factorial(8) == 8 * factorial(7)
        2. factorial(7) == 7 * factorial(6)
            3. factorial(6) == 6 * factorial(5)
                4. factorial(5) == 5 * factorial(4)
                    5. factorial(4) == 4 * factorial(3)
                        6. factorial(3) == 3 * factorial(2)
                            7. factorial(2) == 2 * factorial(1)
                                8. factorial(1) == 1
                            7. factorial(2) == 2 * 1 == 2
                        6. factorial(3) == 3 * 2 == 6
                    5. factorial(4) == 4 * 6 == 24
                4. factorial(5) == 5 * 24 == 120
            3. factorial(6) == 6 * 120 == 720
        2. factorial(7) == 7 * 720 == 5040
    1. factorial(8) == 8 * 5040 == 40320

http://coliru.stacked-crooked.com/a/02e804b483393271