Experiment 14: Increment and Decrement Expressions

There are other assignments that occur so commonly, C++ provides special operators for them, too. For example, if x and y are integer variables, then in place of having to write

x = x + 1;

and

y = y - 1;

C++ allows us to write

x++;

and

y--;

The operators ++ and -- are called the increment and decrement operators, respectively. Each has two forms: the prefix form and the postfix form. When used as a statement:

++x;

or

x++;

the prefix and postfix forms are equivalent. Their difference is in the value produced by the operator. Below is an experiment designed to help determine the difference:

   int x1,
       x2,
       prefixResult,
       postfixResult;

   cin >> x1;            // input a value
   x2 = x1;              // make a copy
   prefixResult = ++x1,  // save result of prefix form
   postfixResult = x2++; // save result of postfix form
                         // display results
   cout << " x1: " << x1 << " x2: " << x2 << endl
        << " prefix produced: " << prefixResult 
        << " postfix produced: " << postfixResult 
        << endl;

The decrement operator (--) works in exactly the same fashion, except that it subtracts 1 from its operand, instead of adding one.

You should now be aware of the C++ shortcuts for the increment and decrement operations, and also understand how the prefix version of each operator differs from the postfix version.

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