Factorization algorithm in C

Question

When creating a number factor algorithm with while I see that by input of the number 21 onwards, the result is wrong -negative.

#include <stdio.h>

long int i=1, ii=1, num, fat=1, somatorio;

int main (){

  while(i <=  5){
    printf("Insira um número: ");
    scanf("%ld", &num);

    ii = 1;
    fat = 1;
    
    while(ii <= num){
      fat = fat * ii;
      ii++;
    }

    printf("Fatorial: %ld\n",fat);

    somatorio = fat + somatorio; 

    i++;

  }
    printf("\nSomatório dos fatoriais: %ld\n\n", somatorio);
}

The program should read 5 numbers and at the end present the sum of factorial.

Answer 1

The negative value that is returning from the factorial is because the variables are being declared as type "long int" which has an interval of (-2.147.483.648 to 2.147.483.647), in which case to circumvent the error uses the long int unsigned data type which has the longest interval

Follow the corrected code:

#include <stdio.h>

unsigned long long int i=1, ii=1, num, fat=1, somatorio;

int main (){

while(i <=  5){
    printf("Insira um número: ");
    scanf("%ld", &num);

    ii = 1;
    fat = 1;

    while(ii <= num){
      fat = fat * ii;
      ii++;
    }

    printf("Fatorial: %llu\n",fat);

    somatorio = fat + somatorio;

    i++;

}
    printf("\nSomatório dos fatoriais: %llu\n\n", somatorio);
}

The factorial number limit is 20! after that number exceeds the 64 bits proposed by the long int unsigned data type.