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Infinite Loop

Discussion in 'C' started by chemr2, Oct 26, 2009.

  1. chemr2

    chemr2 New Member

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    I have taken c++ but it has been about a year ago. I am taking mechanics of materials now and need to solve a bending moment problem. I am trying to get values of Sigma when a is between 0 and 20mm in 2mm increments. I have wrote a little bit of code and need to figure out if this would the correct approach? Also why is this loop infinite?
    I do not have a copy of my text anymore so any help would be appreciated.

    The equation I am solving for is Sigma = MC / I
    Remember I need 16 values for Sigma when a is varying.

    Code:
    #include<iostream>
    #include<cmath>
    using namespace std;
     
    int main()
    {
     
        double n,M,C,I,Sigma,b,h,a,x,i;
     
        n = 2.66;
        C = .020;
        M = 1500;
     
        for(a=0;a<=.020;a+.002)
        {
     
               Sigma = (1500 * .020)/ ((1/12)*(.060)*pow(.040-2*a,3));
               cout<<Sigma<<endl;
         };
     
     
     
     
        system("pause");
        return 0;
     
    }
     
     
     
     
    
     
  2. xpi0t0s

    xpi0t0s Mentor

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    The loop does not modify a. Look carefully at the 3rd clause in the for statement.
     
  3. chemr2

    chemr2 New Member

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    So a+.002 should be what I have listed below in red? If this is the case. I am still getting garbage answers.

    Code:
     
    #include<iostream>
    #include<cmath>
    using namespace std;
     
    int main()
    {
     
        double n,M,C,I,Sigma,b,h,a,x,i;
     
        n = 2.66;
        C = .020;
        M = 1500;
     
        for(a=0;a<=.020;[B][COLOR=red]a+=.002[/COLOR][/B])
        {
     
               Sigma = (1500 * .020)/ ((1/12)*(.060)*pow(.040-2*a,3));
               cout<<Sigma<<endl;
         };
     
     
     
     
        system("pause");
        return 0;
     
    }
    
     
  4. xpi0t0s

    xpi0t0s Mentor

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    What answers do you get and what answers do you expect?
    Do you get different answers if you add ".0" to the end of each integer in the expression?
    Code:
    Sigma = (1500.0 * .020)/ ((1.0/12.0)*(.060)*pow(.040-2.0*a,3.0));
    
     
  5. SaswatPadhi

    SaswatPadhi ~ Б0ЯИ Τ0 С0δЭ ~

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    Probably, he was getting all values as "Infinity".

    @chemr2 :
    The problem is because of the 1/12 in the denominator.

    Both 1 and 12 are integers. Change at least one of them to float to get proper results.
    This should be sufficient :
    Code:
    Sigma = (1500.0 * .020)/ ((1.0/12)*(.060)*pow(.040-2.0*a,3));
    BTW, this is NOT what we call an infinite loop.
    Your loop is finite, but the output values are infinite ;)
     

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