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Question

Hello guys I am new in C++ I am trying to write the function to calculate the second moment of inertia and set the precision with 3 decimal places. In the output does not apply the 3 decimal places in the first call but the following 4 calls does applied. Here is my codes , please help me find the error and if possible please explain some details thank you very much !

double beamMoment(double b, double h) //the function that calculating the second moment of inertia
{
    double I;  //variables b=base, h=height, I= second moment of inertia

    I = b * (pow(h, 3.0) / 12); // formular of the second momeent of inertia


    ofs << "b=" << b << "," << "h=" << h << "," << "I="  << I  << setprecision(3) << fixed <<  endl;
    ofs << endl;


    return I;

}

int main()
{
    beamMoment(10,100);
    beamMoment(33, 66);
    beamMoment(44, 88);
    beamMoment(26, 51);
    beamMoment(7, 19);
    system("pause");
    return 0;
}

The output in my text file is as follow :

b=10,h=100,I=833333 

b=33.000,h=66.000,I=790614.000 

b=44.000,h=88.000,I=2498730.667 

b=26.000,h=51.000,I=287410.500 

b=7.000,h=19.000,I=4001.083 

Answer 1

You have to set stream precision before printing a number.

ofs << 5.5555 << setprecision(3) << endl; // prints "5.5555"
ofs << setprecision(3) << 5.5555 << endl; // prints "5.555"

Stream operators << and >> are, in fact, methods that can be chained. Let's say we have a piece of example java code like:

dog.walk().stopByTheTree().pee();

In C++, if we'd use stream operators, it'd look like:

dog << walk << stopByTheTree << pee;

Operations on dog objects are executed from left to right, and the direction of "arrows" doesn't matter. These method names are just syntactic sugar.

Look here for more details.