getting wrong result with my program

[buldogao87]

program will approximate the value of e...when x=5.7.. but i am not getting the result right . could anybody help me and show my mistake please...
x=1+1/1!+1/2!+1/3!+1/4!+1/5!+.......
when the difference between two successive approximations is less tan 10e-9

int main()
{
double x,myexp1,myexp2,expx,fact,i;
fact=1;
ofstream output("e:result12.dat");
cout<<" ....."<<endl;
output<<" ..... "<<endl;
x=5.7;
myexp1=1;
myexp2=x;
i=2;
expx=myexp1+myexp2;
while (fabs(expx-myexp1 >= 10e-9))
       {
       fact=fact*1;
       myexp1=expx;
       expx=expx+pow(x,i)/fact;
       i=i+1;
       cout<< "..... " <<"i= "<<expx<<endl;
       output<< ".... " <<"i= "<<expx<<endl;
       }


      system("PAUSE");
      return 0;
}

[Philip Nicoletti]

Your factorial is incorrect :

fact = fact * 1;   // should be fact*i

[VictorN]

int main()
{
double x,myexp1,myexp2,expx,fact,i;
fact=1;
ofstream output("e:result12.dat");
cout<<" ....."<<endl;
output<<" ..... "<<endl;
x=5.7;
myexp1=1;
myexp2=x;
i=2;
expx=myexp1+myexp2;
while (fabs(expx-myexp1 >= 10e-9))
       {
       fact=fact*1;

       myexp1=expx;
       expx=expx+pow(x,i)/fact;
       i=i+1;
       cout<< "..... " <<"i= "<<expx<<endl;
       output<< ".... " <<"i= "<<expx<<endl;
       }


      system("PAUSE");
      return 0;
}

The red line doesn't make any sense!
Did you mean

       fact=fact * i;

// Edit: Wow! Philip was faster!

[buldogao87]

yes ... Thanks so much...

[Eri523]

This is also incorrect:

while (fabs(expx-myexp1 >= 10e-9))

It should be:

while (fabs(expx-myexp1) >= 10e-9)

Without that change I get an error C2668. BTW: If the compiler would tolerate the wrong statement, it would even work, since e is approached from below...

But I had to make some more changes to your program to actually compile and correctly calculate the (approximate) value of e. And only that way it matches the approximation formula from post #1. Here is the corrected version, with the changes marked in red:

#include <iostream>
#include <iomanip>
#include <fstream>
#include <math.h>

using namespace std;

int main()
{
double /* x, */myexp1,myexp2,expx,fact,i;
fact=1;
ofstream output("e:result12.dat");
cout<<" ....."<<endl;
output<<" ..... "<<endl;
// x=5.7;  // That's not needed anymore
myexp1=1;
myexp2=1;
i=2;
expx=myexp1+myexp2;
cout << setprecision(12);  // In order to see all changes up to the last iteration
output << setprecision(12);  // ditto
while (fabs(expx-myexp1) >= 10e-9)
       {
       fact=fact*i;
       myexp1=expx;
       expx=expx+1.0/fact;
       i=i+1;
       cout<< "..... " <<"i= "<<expx<<endl;
       output<< ".... " <<"i= "<<expx<<endl;
       }


      system("PAUSE");
      return 0;
}

I hope I didn't miss any change.

... And I hope this wasn't homework I now have done for you...