There is an important difference betwen the prefix and postfix versions of the increment operator, for instance, between ++i and i++. Both will increment i, but they differ in the value produced by the expression. When the value is not used, they are the same, so the statements ++i; and i++; are identical. They differ when the value is used, often in a test.

• i++ returns the old value of i, before incrementing.
• ++i returns the new value of i, after incrementing.

When an expression operator does something more than produce a value, that extra work is called a side effect. The expressions ++i and i++ have different values but the same side-effect.