285: Mainline

So far, you have learned how to use if-else statements to execute one of two embedded computation-performing statements. You should also know about C++'s conditional operator, which enables you to compute a value from one of two embedded, value-producing expressions.

The conditional operator sees frequent service in output statements, where it helps you to produce the proper singular–plural distinctions. Consider, for example, the following program, which displays a temperature change:

#include  
main ( ) { 
  int change; 
  cin >> change; 
  if (change == 1)  
     cout << "The temperature has changed by " 
          << change << " degree." << endl; 
  else 
     cout << "The temperature has changed by " 
          << change << " degrees." << endl; 
} 
--- Data ---
1 
--- Result --- 
The temperature has changed by 1 degree. 

The program works, but most C++ programmers would be unhappy because there are two separate output statements that are almost identical. Such duplication makes programs longer, and the longer a program is, the greater the chance that a bug will creep in.

Accordingly, it would be better to move the variation—the part that produces either the word degree or the word degrees—into a value-producing expression inside a single output statement.