how to avoid rounding?

This is a discussion on how to avoid rounding? within the C Programming forums, part of the General Programming Boards category; Hello, people. I need help. I need to write a program in C that uses a function to calculate the ...

  1. #1
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    how to avoid rounding?

    Hello, people. I need help.

    I need to write a program in C that uses a function to calculate the sum of all fractions 1/(a^4) for "a" values from 1 to x(which is scanf'ed), with 6 digits after the comma. I wrote the code:

    Code:
    #include <stdio.h>
    float f;
    int function(int x) {
    	int a=1;
    	float e;
    	while(a<=x)
    	{
    		e=1/(a*a*a*a);
    		f=f+e;
    		a++;
    	}
    	return(f);
    }
    The code seems to work (it works if I remove "1/", it DOES sum up all a^4's), but in the aforementioned case the answer is always 1.000000. The program seems to automatically round all values of 1/a*a*a*a to zero for a>1. How do I avoid this?

    Thanks in advance
    Last edited by Eldente; 01-27-2011 at 12:59 PM.

  2. #2
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    You're asking your function to return an int, but you're actually trying to return a float. Your compiler should be screaming bloody murder. Listen to it, and heed it's warnings. You might want to use a double for extra precision, since 1/a^4 can get real small real fast.

  3. #3
    -bleh-
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    you need float or double to do division without the answer being truncated. So, you could either declare "a" to be "float" or double, or cast a^4 to float or double. And "1" need to be "1.0" to avoid implicit cast.
    Last edited by nimitzhunter; 01-27-2011 at 01:09 PM.
    "All that we see or seem
    Is but a dream within a dream." - Poe

  4. #4
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    Thanks for your quick answers, my compiler (Visual Studio '10) didn't scream at all, but changing it to float function(int x) did do the trick!

    Thanks again!

  5. #5
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    Quote Originally Posted by Eldente View Post
    Thanks for your quick answers, my compiler (Visual Studio '10) didn't scream at all, but changing it to float function(int x) did do the trick!

    Thanks again!
    It wouldn't give you the error because it does implicit conversion to int for you.
    "All that we see or seem
    Is but a dream within a dream." - Poe

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