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calculating e

This is a discussion on calculating e within the C Programming forums, part of the General Programming Boards category; hello, I have to calculate the mathetical e. So I have this : Code: */ #include <stdio.h> int main ( ...

  1. #1
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    calculating e

    hello,

    I have to calculate the mathetical e.
    So I have this :
    Code:
     */
    
    
    #include        <stdio.h>
    
    
            int
    main ( int argc, char *argv[] )
    {
            int n, teller ;
            float  uitkomst=0;
            printf ("Enter n : ");
            scanf ("%d", &n);
            printf( "n is : %d ", n);
            for (teller=1; teller <=n; teller++)
                    {
                            uitkomst = 1 / teller;
                            printf (" uitkomst  is : %f \n", uitkomst);
                    }
            printf ("e is ongeveer : %f", uitkomst);
    return 0 ;
    }                               /* ----------  end of function main  ---------- */
    But the rule uitkomst = 1/ teller gives as output always zero and not 1/2 , 1/3

    What am I doing wrong now.

    Roelof

  2. #2
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    You'll find out the hard way that c really sucks when you try to mix integers and floats.

    Try this:


    Code:
    uitkomst = 1.0 / teller;

  3. #3
    Captain Crash brewbuck's Avatar
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    That algorithm does not compute e, don't understand why you think it does
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  4. #4
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    I'm hoping he simplified it to demonstrate the issue he was having with mixing floats and ints.

  5. #5
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    Hello,

    I have simplified things because they don't work.

    The right formula is : 1 + 1/1 + 1/(1*2) + 1/ (1*2*3) + 1/ (1*2*3...*n)

    Roelof

  6. #6
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    Integer Division
    Integer Division and Modulus

    Use 1.0 instead of 1 as mentioned in mike65535 post.

    Tim S.

  7. #7
    ATH0 quzah's Avatar
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    Code:
    e = d + 1
    That's how I calculate e.


    Quzah.
    claudiu likes this.
    Hope is the first step on the road to disappointment.

  8. #8
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    This is not the way to calculate e, first of all you will end up with 1/n and you don't need the loop. You must first write a function that calculates the factorial of x " fact(x) " and then change:
    uitkomst = 1 / teller;
    to:
    uitkomst += 1 / fact(teller);

  9. #9
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    Quote Originally Posted by h_dog View Post
    This is not the way to calculate e, first of all you will end up with 1/n and you don't need the loop. You must first write a function that calculates the factorial of x " fact(x) " and then change:
    uitkomst = 1 / teller;
    to:
    uitkomst += 1 / fact(teller);
    This is not the most efficient way; using a loop is better.
    But, yours is a good and easier to understand way.
    But you should use "1.0 /" instead of "1/"

    Tim S.

  10. #10
    Registered User claudiu's Avatar
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    I think you are better off calculating, or more likely, approximating the value of e from the definition of e: lim((1+1/n)^n) where n->infinity. This way you avoid calculating a ton of factorials for no reason. Once you get to a high enough n where you are starting to get the correct value of e, you should experiment with calculating the difference between f(n+1) - f(n) to see if the difference tends to be 0. (where f(n) = (1 + 1/n)^n )
    1. Get rid of gets(). Never ever ever use it again. Replace it with fgets() and use that instead.
    2. Get rid of void main and replace it with int main(void) and return 0 at the end of the function.
    3. Get rid of conio.h and other antiquated DOS crap headers.
    4. Don't cast the return value of malloc, even if you always always always make sure that stdlib.h is included.

  11. #11
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    Personally, if I had to compute e, I would do this
    Code:
    #include <math.h>
    
    int main()
    {
        double e = exp(1.0);
    }
    The precision is naturally limited to the machine precision of a double. But so is any other iterative approach that makes use of a double.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

  12. #12
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    Hello,

    Everybody thanks for the help.
    I have to use loops because im now reading the chapter about loops.

    Roelof

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