C++ How to use relative error with `cout`?

Question

While preparing for my first ever coding interview I found a question where I was requested to print a double number with an absolute or relative error of 10^(-6).

How can I do something like that with cout?

double test_var; // Holding Some value which changes according to my program.
cout << test_var << endl;

Plus, In the expected output I saw numbers like 1000.00 how can I print those .00 too?

Answer 1

You could have used std::setprecision.

#include <iostream>
#include <iomanip>
int main()
{
  double f =3.14159;
  std::cout << std::setprecision(5) << f << '\n'; //prints 3.1416
  std::cout << std::setprecision(9) << f << '\n'; //prints 3.14159
  std::cout << std::fixed;   //Modifies the default formatting for floating-point input/output.  
  std::cout << std::setprecision(5) << f << '\n'; //prints 3.1416
  std::cout << std::setprecision(9) << f << '\n'; //prints 3.141590000   
}