Setting precision of floating point number

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

Try ofs << setprecision(3) << fixed << "b=" << b << "," << "h=" << h << "," << "I=" << I << endl; — John D
– John D, Commented Jun 25, 2016 at 20:03

Jezor · Accepted Answer · 2016-06-25 20:16:51Z

2

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.

answered Jun 25, 2016 at 20:16

Jezor

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1 Comment

kkcc898 Over a year ago

Ya I tried to put that before print the numbers and it works thank you a lot

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