Expert: vijayan - 11/4/2008

Question
Write a program that estimates the value of the mathematical constant e by using the formula:

e = 1 + 1/1! + 2/2! + 3/3! + 4/4! + ………+ n/n!

Here is what i've done::
//Sarah Jamal Qaffaf
//200758855

#include <iostream.h>
int main ()
{
  double x , f=1 , n ,i ,r ,s=0;
  cout<<"Enter a number";
  cin>>n;
  x=1;
  while (x<=n)
  {
  f=f*x;

  i=0 ;
  while (i<=x)
  {
     r=n/f;
  
     i++;
  }
  s=s+r;
  x++;
  }   
  cout<<"e="<<s;
  return 0;
}



Can you tell me what I'm doing wrong??


Answer
indent your code. makes it much easier to read and modify.

unless you are using an obsolete compiler, do not use <iostream.h>. it is not part of standatd C++. instead write: #include <iostream> ; and if you want, using namespace std ;

use appropriate variable types. eg. int for integer values

give meaningful names to variables. for example:
int cnt - the number of terms evaluated so far
int max_cnt - the total number of terms to be evaluated
double factorial - factorial of cnt
double term - the term in the series ie. cnt / factorial
double sum - sum of the terms in the series; at the end, it becomes (approximately) the mathematical constant 'e'

you require only one loop, not two.
each time through the loop:
     evaluate the new factorial - (previous) factorial * cnt
     compute the term - cnt / factorial
     add the term to the sum - sum = sum + term
     increment cnt

#include <iostream>
//using namespace std ;

int main ()
{
 int cnt = 1 , max_cnt ;
 double  factorial = 1.0 , sum = 0.0 ;

 std::cout << "Enter a number " ;
 std::cin >> max_cnt ;
 
 while ( cnt <= max_cnt )
 {
   factorial = factorial * cnt ;
   double term = cnt / factorial ;
   sum = sum + term ;
   cnt++;
 }
 std::cout << "e=" << sum << '\n' ;
}