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13. 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.

  • To improve data accuracy display, the precision can be changed by setprecision(n) manipulator, or by calling precision( ) member function of the stream: 

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