16. Floating-point Precision

Floating-point values are printed with exact fraction part, as specified by the precision.

In default notation format, the precision specifies max number of meaningful digits to display both before and after the decimal point.

The default precision is 6 digits.

This means that the value is rounded to the best approximation while using 6 digits.

If necessary, the default format may change to scientific notation to preserve most accurate representation.

Precision can be changed by calling precision( ) member function of the stream to improve data accuracy:

#include <iostream>
int main()
{
  const double PI = 3.1415926;
  std::cout.precision( 7 );
  std::cout << PI << '\n';
  return 0;
}
/*
Output: 3.141593
*/