Increment Decrement Operators

We have seen that in while, do-while and for loop we write a statement to increase the value of a variable. For example, we used the statements like counter = counter + 1; which adds 1 to the variable counter. This increment statement is so common that it is used almost in every repetition structure (i.e. in while, do-while and for loop). The C language provides a unary operator that increases the value of its operator by 1. This operator is called increment operator and sign ++ is used for this. The statement counter = counter + 1; can be replaced with the statement

counter ++ ;

The statement counter++ adds 1 to the variable counter. Similarly the expressions i = i + 1 ; and j = j + 1 ; are equivalent to i++ ; and j++; respectively. There is also an operator -- called decrement operator. This operator decrements, the value of its operand by 1. So the statements counter = counter - 1; and j = j - 1; are equivalent to counter--; and j--; respectively.

The increment operator is further categorized as pre-increment and post-increment. Similarly, the decrement operator, as pre-decrement and post-decrement.

In pre-increment, we write the sign before the operand like ++j while in post-increment, the sign ++ is used after the operand like j++. If we are using only variable increment, pre or post increment does not matter. In this case, j++ is equivalent to ++j. The difference of pre and post increment matters when the variable is used in an expression where it is evaluated to assign a value to another variable. If we use pre-increment ( ++j ), the value of j is first increased by 1. This new value is used in the expression. If we use post increment ( j++ ),the value of j is used in the expression. After that it is increased by 1. Same is the case in pre and post decrement.

If j = 5, and we write the expression

x = ++ j ;

After the evaluation of this expression, the value of x will be 6 (as j is incremented first and then is assigned to x). The value of j will also be 6 as ++ operator increments it by 1.

If j = 5, and we write the expression

x = j++ ;

Then after the evaluation of the expression, the value of x will be 5 (as the value of j is used before increment) and the value of j will be 6.
The same phenomenon is true for the decrement operator with the difference that it decreases the value by 1. The increment and decrement operators affect the variable and update it to the new incremented or decremented value.

The operators ++ and -- are used to increment or decrement the variable by 1. There may be cases when we are incrementing or decrementing the value of a variable by a number other than 1. For example, we write counter = counter + 5; or j = j – 4;. Such assignments are very common in loops, so C provides operators to perform this task in short. These operators do two things they perform an action (addition, subtraction etc) and do some assignment.

These operators are +=, -=, *=, /= and %=. These operators are compound assignment operators. These operators assign a value to the left hand variable after performing an action (i.e. +, -, *, / and %). The use of these operators is explained by the following examples.

Let’s say we have an expression, counter = counter + 5;. The equivalent of this expression is counter += 5;. The statement counter += 5; does two tasks. At first, it adds 5 to the value of counter and then assigns this result to counter. Similarly the following expressions

can be written in equivalent short statements using the operators ( +=, -=, *=, /=, %= ) as follows

Note that there is no space between these operators. These are treated as single signs. Be careful about the operator %=. This operator assigns the remainder to the variable. These operators are alternate in short hand for an assignment statement. The use of these operators is not necessary. A programmer may use these or not. It is a matter of style.