[NEWBIE] Trying to find the value of 'e'

[prominababy]

i'm still new at this, so i really need your help.

basically i try to find the value of this equation :

e = 1 + 1/1! + 1/2! + 1/3! +.......

i already find the formula to find final the value of factorial :

while ( value1 > 0) { 
	
       
		var1 = var2 * value1--; 
		result = result * var1; 
		
		}

but i wasn't able to get the code to work. this is how i did so far :

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

main ()
{
	int a, b = 0, c = 1, d = 0, e = 0, f = 1, D = 0;
	
	while ( a > 0 ) { /* loop for the whole formula
	
		do { /* loop for the factorial */
		
			D = d;
			b = c * d--; 
			f = f * b;
			} while ( d > 0 );
		
		a = 1 / f;
		e = e + a;
		D++;
		}
		
		printf ( "%d", e );
	return 0;
	}

where did i messed up ? what should i change ? I already tried diffrent version, and this one is the closest i get... At lease that is what i think....

[tabstop]

1 / f is always zero. Maybe 1.0 / f is what you want; or better yet, make f a double value as well, since an int overflows at less than 20!. (Note also that you'll have to reset f to 1 before every time you start your do-while loop (not every run through the loop itself, but when you compute a different factorial).

[master5001]

Have you learned about for loops yet, prominababy? It may be a valid alternative to your factorial loop.

Example:

int main(void)
{
  int i, f[3] = {0,1,0};

  for(i = 0; i < 20; i++)
  {
    f[2] = f[0] + f[1];
    f[0] = f[1];
    f[1] = f[2];
    printf("&#37;d ", f[2]);
  }

  return 0;
}

Obviously this is a Fibonacci sequence, not a factorial. But since everyone is complaining about answering questions directly as of late, I think its a suitable example of a for loop.

[prominababy]

i already try with the looping with for. But the results ends up dapending on how many times i loop it. If i loop it for 3 times than the result is 3 and if i loop it for 4 times than the result is also 4. here is how i done so far, i'm sorry, not very tidy :

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

int main ()
{

	int a, b, c, d = 1, f = 0;
	float g, h = 0, e = 1 ;
	
	for ( a = 0; a <= 5; a++ ) {
	
		f = b;
		
		while ( b > 0 ) {
		
			c = d * b--;
			e = e * c;
			}
	
		g = 1.0 / e;
		h = h + g;
		f++;
		}
		
		
		printf ("the result is %.2f", h);
		getchar ();
		return 0;
	
	}

[master5001]

Not very tidy, indeed. At least your loop is much cleaner now, thank you. I saw someone mentioned the overflow issues with doing factorials, why have you not addressed them?

By the way, b is never initialized nor is it ever reset.

[prominababy]

haha ! i found the mistake ! And it's a very annoying one...

all i have to do was change the f = b into b = f.

thx for the looping with for tip ! Cheers mate !

[master5001]

Example:

int factorial(int base, float *result)
{
  if(base < 13 && result)
  {
    for(*result = 1;base;--base)
      *result *= base;
    return 1;
  }

  return 0;
}

// usage
if(factorial(b, &e))
{
  // do stuff
} else
{
  fputs("Integer overflow!", stderr);
}