How To Round Off A Number

February 18, 2009

Sometimes, it is needed to round off a number to some decimal digits.  Again stringstream comes to help us with the aid of iomanip function setprecision. Following is a sample function to round off a number to a fixed digits.

double Round(const double value, const int digits)
   stringstream stream;
   // Store the number with required no. of decimal
   // places to stream
   stream << setprecision(digits) << value;
   // Convert stream to number
   double roundedValue = 0.0;
   stream >> roundedValue;
   return roundedValue;

The header files sstream and iomanip are needed for the above.

Please note that the variable value holds the number with original no. of decimal places and digits is the total number of digits needed (including the non-decimal digits) after rounding has taken place.

Round(10.37665, 3) gives 10.4 and Round(10.3745, 4) gives 10.37.


If you want to store the number in scientific notation in stream, you can do

stream <<  scientific;

For fixed point format, do

stream <<  fixed;