Question

^{#include <iostream>}

^{#include <cmath>}

^{#include <iomanip>}

^{#include <cstdlib>}

^{using namespace std;}

^{bool isInt (double value) {}

    ^{double dummy;}

    ^{return bool(modf(value, &dummy) == 0);}

^}

^{double sqr(double value) {}

^{return value * value;}

^}

^{double calcFrictionFactor(double R, double D, double epsilon)}

^{

    ^{const double BlasiusCoefficient = 0.3164;}

    ^{double f_old, f_new;}

    ^{f_new = BlasiusCoefficient * pow(R, -0.25);}

^{// loop until our two values are within 0.000001 of each other}

    ^{do {}

  ^{f_old = f_new; // previous guess is now the old one}

  

      ^{// plug guess into the right hand side of the ColeBrook formula}

      ^{f_new = 0.25 * pow(log10((epsilon/D)/3.7 + 2.51 / (R*sqrt(f_old))), -2);}

    ^{} while (fabs(f_new - f_old) > 0.000001);}

    ^{return f_new;}

^}

^{double calcReynolds (double rho, double V, double D, double mu ) {}

^{double R;}

^{R = (rho*V*D)/mu;}

^{return R;}

^}

^{double calcPressureLoss(double V, double L, double D, double rho, double mu, double epsilon) {}

^{double R;}

^{double f;}

^{double Delta;//pressure loss}

^{R = calcReynolds (rho, V, D, mu);}

^{if (R<3500){}

^{return -1;}

^}else{

^{f = calcFrictionFactor (R, D, epsilon);}

^{Delta = (f)*(L/D)*(rho)*((pow(V,2)/2));}

^{return Delta;}

^}

^}

^{void printTable(double V, double L, double rho, double mu, double epsilon){}

^{double x;}

^{int i;}

^{double Delta;}

^{double D;}

^{Delta = calcPressureLoss(V, L, D, rho, mu, epsilon);}

^{cout<<"Diameter (m)          Pressure Drop(Pa)"<<endl;}

^{cout<<fixed<<showpoint;}

^{for (i = 0; i<15; i++){}

^{x = (i+1)*0.05;}

^{cout<<setw(12)<<setprecision(2)<<x<<setw(12)<<setprecision(1)<<Delta<<setw(12)<<endl;}             

^}

^}

^{int main (void) {}

^{const double rho = 998.2;}

^{double V;}

^{double L;}

^{double D;}

^{const double mu = 1.002e-3;}

^{const double epsilon = 0.045;}

^{double R;}

^{double Delta;}

^{double x;}

^{cout<<"Enter the value (-1 -1 to stop): ";}

^cin>>V>>L;

^{while (V!=-1&&L!=-1){}

^{if (V<0||L<0){}

^{cout<<"error"<<endl;}

^}else{

^{printTable(V, L, rho, mu, epsilon);}

^{Delta = calcPressureLoss(V, L, D, rho, mu, epsilon);}

^}

^{cout<<"Enter the value (-1 -1 to stop): ";}

    ^cin>>V>>L;

^}//endwhile

    ^{system("PAUSE"); return 0;}

^}

Need help.After compilation, the Pressure Drop should show the corresponding results, but Pressure Drop just keeps showing - 1. I try to debug it, and the program in highlight place cannot execute the content in else although the if conditions cannot be met.

Answer 1

The variable D is passed as an argument without any initialization to the function calcPressureLoss from printTable function.

Hence a value like 6.91141e-310 is assigned to D and because of this, value like 1.37704e-303 is getting assigned to R which is less than 3500 for the first time when input values for V and L are entered.

Also in function main after calling printTable function, calcPressureLoss function is getting called with the variable D as an argument which is again not initialized. Hence in the function calcPressureLoss, value of D is assigned to 0. Hence value of R also becomes 0 for rest of the input values for V and L until -1 -1 is entered for them which meant to stop executing.

Thus if a proper value is initialized to D, this problem will be solved.