Number

Number Formatting

A programmer can adjust the way that output appears, a task known as output formatting. The main formatting approach uses manipulators. A manipulator is an item designed to be used with the insertion operator << or extraction operator >> to adjust the way output appears, and is available via #include <iomanip>; or #include <ios>; in namespace std. For example, cout << setprecision(3) << myFloat; causes the floating-point variable myFloat to be output with only 3 digits; if myFloat was 12.34, the output would be 12.3. . Most manipulators change the state of the stream such that the manipulation affects all subsequent output, not just the next output.

Manipulator	Description	Example
fixed	Use fixed-point notation. From <ios>	12.34
scientific	Use scientific notation. From <ios>	12.3E+01
setprecision(p)	If stream has not been manipulated to fixed or scientific: Sets max number of digits in number	p=3 yields 12.3 p=5 yields 12.34
	If stream has been manipulated to fixed or scientific: Sets max number of digits in fraction only (after the decimal point). From <iomanip>	fixed: p=1 yields 12.3 scientific: p=1 yields 1.2e+01
showpoint	Even if fraction is 0, show decimal point and trailing 0s. Opposite is noshowpoint. From <ios>	For 99.0 with precision=2 and fixed: 99 (default or noshowpoint) 99.00 (showpoint)

#include <iostream>
#include <ios>
#include <iomanip>
using namespace std;

int main() {
   
   double milesTrvld = 765.4321;
   
   cout << "setprecision(p) -- Sets # digits" << endl;
   cout << milesTrvld << " (default p is 6)" << endl;
   cout << setprecision(8) << milesTrvld << " (p = 8)" << endl;
   cout << setprecision(5) << milesTrvld << " (p = 5)" << endl;
   cout << setprecision(2) << milesTrvld << " (p = 2)"
        << " (note rounding)" << endl;
   cout << milesTrvld << " (manipulator persists)" << endl << endl;
   
   cout << setprecision(2);
   cout << "(For following, p = 2 applies to fraction only)" << endl;
   
   // fixed -- uses fixed point notation
   cout << fixed;
   cout << "fixed: " << milesTrvld << endl;
   
   // scientific -- uses scientific notation
   cout << scientific;
   cout << "scientific: " << milesTrvld << endl;
   
   return 0;
}