Factorial with recursion

Question

I have to make a program that calculates the factorial of a number using recursiveness within the main.

#include<stdio.h>
#include<stdlib.h>
#include<conio.h>

int main (int argc, char *argv[]){
    float numero;
    int valorA = atoi(argv[1]);
    char var1[10];
    itoa(valorA-1, var1, 10);
    if (valorA <= 1)
        return(1);
    else{
        numero = valorA * main(argc, var1);
        return numero;
    }




    printf("Fatorial de %d = %.2f", atoi(argv[1]), numero);
}

When I pass the number as argument at the command prompt an error occurs, saying that the program has stopped working. What’s wrong with my code?

Answer 1

I used a different strategy to get the number, but as your example does not have the factorial itself, maybe this form is easier for Oce, using the scanf:

#include <stdio.h>
#include<stdlib.h>

int genFatorial(int n) {
    if(n) {
        return n * genFatorial(n - 1);
    } else {
        return 1;
    }
}

int main() {
    int num;
    scanf("%d", &num);

    int fatorial = genFatorial(num);
    printf("%d\n", fatorial);

    return 0;
}

This is a very simple solution to this problem, I suggest you use an auxiliary function instead of calling again the main function too.

I hope I’ve helped!

Answer 2

Presenting another solution to the problem:

#include <stdio.h>
#include <stdlib.h>

int fat (int n)
{
  int res = 1;

  while (n > 1) {
    res = res * n;
    n--;
  }

return res;
}

int main () 
{
  unsigned int n;

  printf("Entre com o valor de n: ");
  scanf("%d", &n);
  printf("Fatorial de %d = %d\n", n, fat(n) );

  system("pause");
  return 0;
}