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Help Needed: Nothing is Printed

Discussion in 'C++' started by Chimera9, Apr 26, 2010.

  1. Chimera9

    Chimera9 New Member

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    Code:
    using namespace std;
    # include <iostream>
    # include <string>
    # include <iomanip>
    # include <vector>
     
    double a;
    double b;
    double h;
     
    double f(double x) {
         return x* - 1;
    }
    double sign(double x) {
         if (x < 0) {
              return 0;
         }
            else {
                 return 1;
            }
    }
    double FindRoot (double a,double b,double h) {
    double s;
    double x;
    s=sign(f(a));
    while (s = sign(f(x))) {
      for (x=0; x < b; x=(a+b)/h)
    return x;
    }
    }
    double root=FindRoot (a, b, h);
    void PrintResults ( double a, double b, double root) {
    cout << "A root of the function f(x)=x^2-1 between " << a << " and " << b << " is " << root << endl << flush;
    }
     
    int main( ) {
    PrintResults (-2,0,0.01);
      return 0;
    }
    I'm unsure why nothing's being printed. I'm guessing something's wrong with the format of PrintResults or my formula for finding the root is incorrect. Help wanted urgently. Thank you.
     
    Last edited by a moderator: Apr 27, 2010
  2. virxen

    virxen New Member

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    one error is this ---> while (s == sign(f(x))) {
    and another is this -->return x*x - 1;
     
  3. Chimera9

    Chimera9 New Member

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    I fixed those errors (thanks for catching those, by the way), but still nothing is being printed.
     
  4. SaswatPadhi

    SaswatPadhi ~ Б0ЯИ Τ0 С0δЭ ~

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    Occupation:
    STUDENT !
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    Orissa, INDIA
    Home Page:
    Found the error :)
    Change :
    Code:
    double root=FindRoot (a, b, h);
    to
    Code:
    double root;
    First, you are trying to initialize a global var root outside any procedure.
    Second, the vars that you pass as args : a, b, h to FindRoot are un-initialized !

    Change the code and it should print.
     
  5. davidk

    davidk New Member

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    Home Page:
    Place this line
    Code:
    double root=FindRoot (a, b, h);
    inside your PrintResults() function, or initialize 'root' variable inside main().
     
  6. virxen

    virxen New Member

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    another error is this

    no need for for command just put return 0; its the same!
    No command is executed after a return!!!

    and of course as davidk and SaswatPadhi said change your code like this

    Code:
    using namespace std;
    # include <iostream>
    # include <string>
    # include <iomanip>
    # include <vector>
     
    [COLOR=Red]//[/COLOR]double a;
    [COLOR=Red]//[/COLOR]double b;
    [COLOR=Red]//[/COLOR]double h;
      .......
    int main( ) {
    [COLOR=Red]double a=-2,b=0,h=0.01;[/COLOR]
        [COLOR=Red]double root=FindRoot (a, b, h);
        PrintResults (a,b,root);[/COLOR]
    .............
    
     
  7. Chimera9

    Chimera9 New Member

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    Thanks for all the help guys! I finally got it right with a little input from my instructor though. But again, thanks for taking the time to help.
     

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