The Decrement operator is a special, immediate operator that decrements a variable by one and assigns the new value to that same variable. It can only be used in run-time variable expressions. Decrement has two forms, pre-decrement and post-decrement, depending on which side of the variable it appears on. The pre-decrement form appears to the left of a variable and the post-decrement form appears to the right of a variable. This is extremely useful in programming since there are many situations that call for the decrementing of a variable right before or right after the use of that variable's value. For example:
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Y := --X + 2 |
The above shows the pre-decrement form; it means "decrement before providing the value for the next operation". It decrements the value of X by one, writes that result to X and provides that result to the rest of the expression. If X started out as 5 in this example, --X would store 4 in X, then the expression, 4 + 2 is evaluated, finally writing the result, 6, into Y. After this statement, X equals 4 and Y equals 6.
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