C Programming factorial outputting wrong values

Question

int main (void)
{
   int i;
   for (i=1; i<=20; i++) {
       int j;
       unsigned long long fac = 1;

       for ( j = 1; j<=i; ++j) {
          fac *= j;
       }

       printf ("%2i! = %ld\n", i, fac);
    }

return 0;
}

From 14! to 20! outputs wrong values.

It either gives a negative number or the number is not big enough.. what is the problem?

Answer 1

printf ("%2i! = %ld\n", i, fac);

The problem is here, use proper notation for unsigned long long type value

Try:

printf ("%2i! = %llu\n", i, fac);

Answer 2

The variable fac is of type unsigned long long . The correct format specifier for this type is is %llu :

printf ("%2i! = %llu\n", i, fac);

Answer 3

You are calculating correctly but printing incorrectly! use %llu :

  printf ("%2i! = %llu\n", i, fac);

  20! = 2432902008176640000

There!