4.5. Increment and Decrement Operators

The increment (++) and decrement (--) operators provide a convenient notational shorthand for adding or subtracting 1 from an object. This notation rises above mere convenience when we use these operators with iterators, because many iterators do not support arithmetic.

There are two forms of these operators: prefix and postfix. So far, we have used only the prefix form. This form increments (or decrements) its operand and yields the changed object as its result. The postfix operators increment (or decrement) the operand but yield a copy of the original, unchanged value as its result:

int i = 0, j;
j = ++i; // j = 1, i = 1: prefix yields the incremented value
j = i++; // j = 1, i = 2: postfix yields the unincremented value

These operators require lvalue operands. The prefix operators return the object itself as an lvalue. The postfix operators return a copy of the object’s original value as an rvalue.