Decrement operator --

The -- (decrement) operator subtracts 1 from the value of a scalar operand, or if the operand is a pointer, decreases the operand by the size of the object to which it points. The operand receives the result of the decrement operation. The operand must be a modifiable lvalue.

You can put the -- before or after the operand. If it appears before the operand, the operand is decremented, and the decremented value is used in the expression. If the -- appears after the operand, the current value of the operand is used in the expression and the operand is decremented. A pre-decrement expression is an lvalue. A post-decrement expression is an rvalue.

For example:

play = --play1 + play2--;

is similar to the following expressions; play1 is altered before play:

int temp, temp1, temp2;

temp1 = play1 - 1;
temp2 = play2;
play1 = temp1;
temp = temp1 + temp2;
play2 = play2 - 1;
play = temp;

The result has the same type as the operand after integral promotion, but is not an lvalue.

The usual arithmetic conversions are performed on the operand.

IBM extension The decrement operator has been extended to handle complex types, for compatibility with GNU C. The operator works in the same manner as it does on a real type, except that only the real part of the operand is decremented, and the imaginary part is unchanged.