Why does my FirstFactorial program keep looping back to while condition even after the condition is not met

Question

Here's the code snippet, this when run with number 4 outputs 2424242448484848288288288288576576576576. Not sure as to why would the execution would jump back to while loop after exiting the function code. Any help will be appreciated. Thank you in advance.

#include <stdio.h>
#include <string.h>

int result = 1;
void FirstFactorial(int);

void FirstFactorial(int num) {
    // code goes here
    while (num > 0) {
        result = result * num;
        num--;
        FirstFactorial(num);
    }
    printf("%d", result);
}

int main(void) {
    int var;
    // keep this function call here
    printf ("Enter your no.\n");
    scanf("%d", &var);
    FirstFactorial(var);
    return 0;
}

Answer 1

Within the function

void
FirstFactorial(int num)
{
  // code goes here
  while(num > 0)
    {
      result = result * num;
      num--;
      FirstFactorial(num);
    }
  printf("%d", result);
}

each its iteration calls itself num times and all iterations together output the global variable result.

So for example in the first call of the function the function calls itself in the while loop for the range of values [num, 1].

Remove the while loop and do not use the global variable.

Here is a demonstrative program.

#include <stdio.h>

unsigned long long int factorial( unsigned long long int n )
{
    return n < 2 ? 1 : n * factorial( n - 1 );
}

int main(void) 
{
    printf( "%llu! = %llu\n", 4llu, factorial( 4 ) );
    printf( "%llu! = %llu\n", 20llu, factorial( 20 ) );

    return 0;
}

The program output is

4! = 24
20! = 2432902008176640000

Pay attention that the maximum value you may specify is 20.