Thread: small program to calculate e

the program goes like this:
it should calculate the value of e^x by the series
1+x+x^2/2!+x^3/3!...+x^n/n!
when the user inputs a value , eps , which the program has to stop compute e^x when x^n/n<eps.

I wrote 2 function , one calculating the factorial result (fact), and one calculates the value x^n/n! (monom).
these functions works well, but the program keeps giving me 1 as result for e^x (or it gets stuck..)
it seems that the problem comes from the condition monom (x,j)<eps, but I can't see why...

Code:

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

float fact (int);
double monom (float x, int n);

int main (void)
{
float x;
printf ("please enter x value for e^x: ");
scanf ("%f", &x); 
double exp=1;
float eps;
printf ("please enter delta: ");
scanf ("%f", &eps);
int j;
for (j=1; monom (x,j)<eps; j++)
exp+=monom (x,j);
printf ("%f",exp);
 
return 0;
}

float fact (int a)
{    
float result=1;
int i;
for (i=1;i<=a;i++)
result*=i;    
return result;    
}

double monom (float x, int n)
{
return (pow(x,n)/fact(n));    
}

can you guys help me? thanks a lot!

Don't you want your loop to terminate once the difference of the successive terms in the series becomes less than epsilon rather than greater than?

Also it seems rather inconsistent that you name your variable eps (suggesting epsilon) and then ask the user to enter delta .

Otherwise though the code is quite good, you need to work on your indentation though and personally I'm not a fan of declaring my variables throughout my code but to each his own.

Originally Posted by DeadPlanet

Otherwise though the code is quite good.

Serious question, what makes it good? To be honest (sorry Dave11, you're learning so I understand) I can't find much good about it.

Originally Posted by Hodor

Serious question, what makes it good? To be honest (sorry Dave11, you're learning so I understand) I can't find much good about it.

The code is not unnecessarily long. All functions and variables have close to reasonable names. Functions are correctly prototyped. Proper standard header files are included. We even have int main( void ) and return 0. These are all things that lots of learning programmers struggle with.

This is not production code and I won't be including it in my own projects but Dave11 is very much on the right track. One of the major obstacles that stand in the way of him becoming a good programmer is quitting too easily. I'm of the belief that encouragement gives people some self-belief and so they are less likely to quit.

I only ever compliment people on things that I think they are actually doing well at (relative to their skill level). I do not just make things up to make people feel good.

I guess it's more fun to be a dickhead towards people though so we can try your idea of telling people their code is bad from now on.

Originally Posted by DeadPlanet

I guess it's more fun to be a dickhead towards people though so we can try your idea of telling people their code is bad from now on.

If you think I was being a dickhead, then you're mistaken. It was an honest question. I don't mince words (often) but at the same time I did not say anything at all about the programmer; I was referring to the code and my comment (question, actually) was purely objective.

Originally Posted by Dave11

kermit: I use dev-c++ , so I do have excess to debugger, but this program has good syntax , but bad logic, so debugger wasn't helpful at the time

That is an interesting statement, as a debugger is useless for syntax errors but excellent for logic errors. I hope you're not thinking of the warnings you get from the compiler as your debugger, because it isn't. A debugger is a program (like gdb) that allows you to step through a program's execution, one step at a time, which will allow you to see when and how your logic errors manifest themselves.

Originally Posted by King Mir

I recommend using a more recent IDE than Dev-C++. The compiler it comes with is very out of date.

At the very least make sure it is the most up to date version. There is a new (forked) version of Dev-C++. You can find it here