Why does my factorial function always return 1?

Question

I'm learning C and came up with this one-line factorial function using a ternary operator on the return, but it always returns 1.

#include <stdio.h>

int factorial(int n){
    return  (n > 1) ? factorial(n -1) : 1;
}

int main() {
    for(int i = 0; i < 10; i++){
        printf("%d factorial is %d\n",i,factorial(i));
    }
    return 0;
}

You can see the code returns 1 for values 0 through 9 in this link: https://code.sololearn.com/c7uSnfxw92sl/#c

Answer 1

That is very easy since we can use the substitution rules. Eg.

factorial(10);                    // ==
(10 > 1) ? factorial(10 - 1) : 1  // ==
(9 > 1) ? factorial(9 - 1) : 1    // ==
(8 > 1) ? factorial(8 - 1) : 1    // ==
(7 > 1) ? factorial(7 - 1) : 1    // ==
(6 > 1) ? factorial(6 - 1) : 1    // ==
(5 > 1) ? factorial(5 - 1) : 1    // ==
(4 > 1) ? factorial(4 - 1) : 1    // ==
(3 > 1) ? factorial(3 - 1) : 1    // ==
(2 > 1) ? factorial(2 - 1) : 1    // ==
(1 > 1) ? factorial(1 - 1) : 1    // ==
1

Your function is broken. It does not multiply n with the result of factorial(n - 1). You could also do it with an accumulator for it to become tail recursion, but you cannot just replace it with factorial(n - 1) since it will not compute the same as factorial(n).

Answer 2

You forgot to multiply by n

int factorial(int n){
    return (n > 1) ? n * factorial(n -1) : 1;
}