Whats wrong with setprecision in my compiler? - c++

Question

I've been having trouble with my compiler, NetBeans. It seems that using setprecision is not doing anything. Here is the code needed to see what's happening. This part of the program check to see if a triangle it possible given three sides.
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){
double SideA,SideB,SideC,p,a,longest;
cout<<"Enter the length of each side of your triangle. Press enter after each number."<<endl;
cin>>SideA>>SideB>>SideC;
cout<<fixed<<setprecision(3);
if(SideA+SideB<=SideC||SideA+SideC<=SideB||SideB+SideC<=SideA||SideA<=0||SideB<=0||SideC<=0)
{
cout<<"The length of the first side is "<<SideA<<"."<<endl;
cout<<"The length of the second side is "<<SideB<<"."<<endl;
cout<<"The length of the third side is "<<SideC<<"."<<endl;
cout<<"This triangle is impossible."<<endl;
}
return 0;
}
My problem is that I want the side length to be rounded to the nearest thousandths when shown on the screen. It does not do this with my NetBeans compiler. I've put this into online compilers, and it works there.
Here's my C++ configuration in NetBeans:
The sample input data is: 6.6666666, 5.4444444, 1
The expected output is: 6.667, 5.443, 1.000
The actual output is: 6.66667, 5.44444, 1

Answer 1

Your code is behaving correctly. You are using cout to display the values of double variables, and by default it will use a precision of 6:
A double value will be printed using a general format that usually
works fine to represent a number in a small amount of space. The basic
amount of space used is determined by the precision. The default
precision is 6, which means up to 6 significant digits are used to
represent the number. This counts digits both to the left and the
right of the decimal point. Fewer digits are printed if the result is
accurate; e.g. trailing zeros at the right of the decimal point are
not printed. As shown in the example below, as the number increases in
size, places to the right of the decimal point will be dropped, and
the result rounded off as needed to stay within 6 digits.
The text in bold font explains the output you obtained for your sample input: 6.66667, 5.44444, and 1.
You can limit the precision to obtain the results you want by using cout.precision() or setprecision(). This is also detailed in the linked article.
Finally, note that this is issue has nothing to do with NetBeans. You can confirm this by using g++ to compile your code from the command line. When you run it you will get the same results, even though you are not using NetBeans.