Question

When I try and round digits using setprecision(2) in C++, numbers like “0.093” re returned- THREE, not two digits after the decimal! I cannot figure out why this is. I’ve included my very rudimentary code below, in case I am severely missing some point. Thanks!

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
    double tax = 0.06 ; //Tax Rate
    float cost ; //Cost of item
    float computed ; //Non-rounded tax

    cout << "Enter the cost of the item: " ;
    cin >> cost ;

    computed = tax*cost;

    cout << "Computed: $" << computed << endl;
    cout << "Charged: $" << setprecision(2) << computed << endl; //Computed tax rounded to 2 decimal places



    return 0;

}

Answer 1

This is because std::setprecision doesn’t set the digits after the decimal point but the significant (aka “meaningful”) digits if you don’t change the floating point format to use a fixed number of digits after the decimal point. To change the format, you have to put std::fixed (documentaion) into your output stream:

cout << "Charged: $" << fixed << setprecision(2) << computed << endl;