Formatting the Output

To format a program's output means to control how it appears visually on the screen or on a printer. We use the special ostream variable cout together with the insertion operator << to accomplish this. Here is what an output statement looks like.

The C++ standard library supplies many manipulators, here are a few of them:

In this table, the manipulators without arguments (such as endl, fixed, showpoint) are available through the header file iostream.
Those with argument (such as setw(n), setprecision(n)) require the header file iomanip.

Now look at an example and see how those manipulators are used: // Program Format demonstrates the use of fieldwidth; // specifications. #include <iostream> #include <iomanip> using namespace std; const int INT_NUMBER = 1066; //define an int constant const float FLT_NUMBER = 3.14159; //define a float constant int main () { float fltValue; //declare a float type variable int intValue; //declare an int type variable //Set all printout in decimal format cout << fixed; intValue = INT_NUMBER + FLT_NUMBER; //Type coercing fltValue = float(INT_NUMBER) + FLT_NUMBER; //Type casting cout << INT_NUMBER << endl; cout << intValue << endl; //reserve 10 character positions for intValue cout << setw(10) << intValue; cout << setw(10) << intValue << intValue /10 << endl; //reserve 10 character positions for fltValue cout << setw(10) << fltValue << endl; //set precision to 4 decimal positions cout << setprecision(4) << fltValue << endl; //reserve 10 character positions for fltValue //and reset precision to 3 decimal positions cout << setw(10) << setprecision(3) << fltValue << endl; cout << fltValue << endl; //print intValue taking as many character positions as needed, //and then reserve 3 character positions for intValue //and then reserve 7 character positions for intValue cout << intValue << setw(3) << intValue << setw(7) << intValue << endl; return 0; }