Hello everyone, this is my first time here on this website and forum, and after reading through some of it, I think it's very helpful, so I would like to say thank you.

I am facing a problem that I have been trying to solve for a few days so far with little success. I'm a beginner in C programming; I just started to learn it about a month ago on my own through some books. I'm mainly using the CodeBlocks program to write my programs.

I recently finished loops and after writing many programs as exercise, I am stuck on one that I just cant do and it is really annoying me. My code keeps getting mixed up and I have no idea how to tie it together to solve the problem. The functions I'm using seem flawed for some reason.

Here is the description of what I need to do:

Write a C program to compute the value of the mathematical constant e to the power of x (ex) by using the infinite series:
ex = 1 + x/1! + x2/2! + x3/3! + x4/4! + …
Your program should include at least one function called compute_ex which receives any value of x as a parameter and returns the value of ex as a result. Your program should also NOT use the already predefined system function pow.
The computation should stop when the new term added ( term = Xn/n! where n=0,1,2,3,…) is less than 0.0001.

Here is my work on it. I appologize for it being kind of messy as the program is incomplete:

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

/* Construct the user-defined functions used */
double compute_ex(double x);
int compute_factorial(int n);
int compute_power(int y);
void instruct_user(void);
void instruct_ending(void);

int main(void)

* Variable declarations */

double exponent;

/* Display user instructions */

instruct_user();

printf("Enter the desired exponent of e^x > e^");
scanf("%lf", &exponent);

double
compute_ex(double x);
{
int n;
int product;

product=1;

while(x<0.0001)
{

for(i=n; i>1;--1)
{
product=product*i}
}

}

}

/* Factorial computation functions */

int
compute_factorial(int n);
{
int i; /* Local variables */
int product_of_factorial; /* Accumulator for product computation */

product_of_factorial=1;

/* Computes the product n x (n-1) x (n-2) x ... x 2 x 1 */

for(i=n; i>1;--i)
{
product_of_factorial=product_of_factoria…

}
/* Returns fuction result */
return(product_of_factorial);
}

/* Power computation functions */

int
compute_power(int y, int a);
{
int j; /* Local variables */
int product_of_power; /* Accumulator for product computation */
int

/* Computes the product n x (n-1) x (n-2) x ... x 2 x 1 */

for(j=a; j>1;--j)
{
product_of_power=y*y;

}
/* Returns fuction result */
return(product_of_power);
}``````

I tried to ask some friends and they suggested the following way of writing the program. However, I find it too advanced for me, as it has something I do not know, and I want to do it more simply, so I can understand it that way before moving to something more advanced.

``````/*  Write a C program that computes the value ex by using the formula

ex= 1 + x/1! + x2/2! + x3/3! + ....

*/

#include<stdio.h>
#include<conio.h>
void main()
{
int n,x,i;
float e=0.0;
long factorial(int); // Prototype declaration
float power(int,int); // Prototype declaration

clrscr();
printf("Enter the value of \'n\': ");
scanf("%d",&n);
printf("Enter the value of \'x\': ");
scanf("%d",&x);
for(i=0;i<=n;i++)
e += power(x,i)/(float)factorial(i);
printf("e^x = %-15.7f",e);
}

// Recursive factorial() function
long factorial(int n)
{
if(n<0)
return 0;
else if(n==0||n==1)
return((long)(1));
else
return((long)(n*factorial(n-1)));
}

// The power() function
float power(int a,int b)
{
int i,flag;
float p=1.0;
if(b<0)
b*=-1,flag=1;
else
flag=0;
for(i=1;i<=b;i++)
p *= a;
if(flag==0)
return p;
else
return (1/p);
}``````

I hope this is correct way of posting a question here since its my first time. Thank you in advance for any help you can provide me with.

OK, your function definitions are causing some errors for me.

Whenever you are simply writing a function prototype, you use a semicolon. But when you are defining a function, you don't.

``````my_prototype( int a, char b );

my_function( int a )
{

}``````

After I did …

The negative values are probably coming from compute_factorial. The numbers there would get pretty large, so the integers are probably overflowing. Along with your changes, I replaced some ints with doubles and everything worked out pretty well.

``````double
compute_factorial(int n);
{
int i;  /* Local variables */ …``````

I'm very happy I was able to help you, d00mhammers. I'm sorry to say that I probably can't teach you much, and I can't suggest any books or references.

Regardless, I wish you the best of luck in your studies. If you ever get stumped on another problem while …

## All 10 Replies

#
for(j=a; j>1;--j)
#
{
#
product_of_power=y*y;
#

#
}

product_of_power=y*y ?
always return square(y)
you should implement product_of_power=product_of_power*y;

I did some fixing to my code and came up with the following:

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

/* Construct the user-defined functions used */
double compute_ex(double x);
int compute_factorial(int n);
int compute_power(int y, int a);

int main(void)
{
/* Variable declarations */

double exponent;
double result;

/* Display user instructions */

instruct_user();

printf("Enter the desired exponent of e^x > e^ ");
scanf("%lf", &exponent);

result = compute_ex(exponent);

printf("\n\n The value of e^ %.2f is \n", exponent, result);

/* Ending notes */

return(0);
}

/* Exponential computation functions */

double
compute_ex(double x);
{

double term;
double sum;
int b;

term = 1.0f;
sum = 1.0f;

for(b = 1; term > 0.0001f; b++)
{
term = (compute_power( x, b))/(compute_factorial(b));
sum = sum + term;

}

return(sum);

}

/* Factorial computation functions */

int
compute_factorial(int n);
{
int i;  /* Local variables */
int product_of_factorial;    /* Accumulator for product computation */

product_of_factorial=1;

/* Computes the product n x (n-1) x  (n-2) x  ... x 2 x 1 */

for(i=n; i>1;--i)
{
product_of_factorial=product_of_factorial*i;

}
/* Returns fuction result */
return(product_of_factorial);
}

/* Power computation functions */

int
compute_power(int y, int a);
{
int j;  /* Local variables */
int product_of_power;    /* Accumulator for product computation */

product_of_power=1;

/* Computes the product of y to the power a (y^a) */

for(j=0; j<a;j++)
{
product_of_power=product_of_power*y;

}
/* Returns fuction result */
return(product_of_power);
}``````

However, I got many errors, can someone help me solve them? I dont know where the problem is, I'm very confused.

P.S. im working using codeblocks.

OK, your function definitions are causing some errors for me.

Whenever you are simply writing a function prototype, you use a semicolon. But when you are defining a function, you don't.

``````my_prototype( int a, char b );

my_function( int a )
{

}``````

After I did that, the code ran OK, but the answer was wrong because it seems to lose precision. I modified the line 53 to `term = ([b]1.0*[/b]compute_power( x, b))/(compute_factorial(b));` ,
and then I got the right answer for e^2.

So overall, your program seems to be working pretty well.

OK, your function definitions are causing some errors for me.

Whenever you are simply writing a function prototype, you use a semicolon. But when you are defining a function, you don't.

``````my_prototype( int a, char b );

my_function( int a )
{

}``````

After I did that, the code ran OK, but the answer was wrong because it seems to lose precision. I modified the line 53 to `term = ([b]1.0*[/b]compute_power( x, b))/(compute_factorial(b));` ,
and then I got the right answer for e^2.

So overall, your program seems to be working pretty well.

Thanks a lot! You are a life saver! It finally worked! After a spend over 4 hours trying to figure out where i was wrong, silly me. However there is a small problem, the program doesnt seem to be accepting any fractions like 2.5 or whatsoever, how can i fix it? And one more thing, how can I add a loop to it and where exactly to make this program reusable? I.E. give you a choice to enter a new value once you are done or a sentinel to stop? Thanks again.

I tried to change this

``````int
compute_power(int y, int a);
{    int j;
int product_of_power``````

to

``````double
compute_power(double y, int a);
{    int j;
doubleproduct_of_power``````

this seems to solve the problem in 2.5 and 3.5, however it makes munbers 4 and above give negative results, so i guess my try didnt work.

The negative values are probably coming from compute_factorial. The numbers there would get pretty large, so the integers are probably overflowing. Along with your changes, I replaced some ints with doubles and everything worked out pretty well.

``````double
compute_factorial(int n);
{
int i;  /* Local variables */
double product_of_factorial;``````

To make the program loop at input, you can try something like this:

``````do
{
printf("Enter the desired exponent of e^x (use '0' to quit) > e^ ");
scanf("%lf", &exponent);

result = compute_ex(exponent);

printf("\n\n The value of e^ %.2f is \n", exponent, result);
} while( exponent != 0 );``````

I hope this helps!

I would like to thank everyone who took time and effort to reply to my request and help me out. I really appriciate it. If anyone would have any advice or tips for me, I would be pleased to recieve them. I have been learning C by myself for about a month so far so there is plenty that I dont know, so anything that would help me learn something new is more than welcome from anyone, as I am trying to learn all I can, and its not as easy for a beginner. Once again thank you all!

P.S.

IsharaComix,

My hat goes off to you! I have been trying to solve this problem for a few days so far, and even asked soem friends, which didnt help, but you did. Thank you very much for your time and effort, I really appriciate everything you done for me. You seem to know a great deal about C programming, perhaps your could teach me a little? I could use all the help I could get. Actually, at the moment, I started to learn about pointers, arrays, and strings, any advice or tips on that? I find them quite confusing since I'm learning by myself. Do you know any good books/references I could study from? Once again thank you very much for everything, cheers mate!

I really like "Let us C" by Yashwant Kanetkar

This book assumes no previous knowledge of programming and teaches C programming in a very step step and methodical manner

I'm very happy I was able to help you, d00mhammers. I'm sorry to say that I probably can't teach you much, and I can't suggest any books or references.

Regardless, I wish you the best of luck in your studies. If you ever get stumped on another problem while learning C, please don't hesitate to start another thread, and I or one of the other fine folks here at DaniWeb will try to help you out.

You can also help US out by marking this thread as solved. ;)

``````#include<stdio.h>
#include<conio.h>
void main()
{  //exponentiial
int i;
float s=1,t=1,x,r;
printf("exponentiel of x Enter the value of x:-");
scanf("%f",&x);
r=x;
for(i=1;i<=25;i++)
{
t=t*i;
printf("%f\n",t);
s=s+r*(1/t);
r=r*x;
}
printf("%f\n",s);
getch();
}
``````

exponent shortest code

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