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Incrementing and Decrementing Variables

If you wanted to add 1 to a variable, you could use the + operator:

count = count + 1;

However, it is unlikely that an experienced programmer would write code like this. Adding 1 to a variable is so common that in C#, you can do it with the ++ operator. To increment the variable count by 1, write the following statement:

count++;

Similarly, subtracting 1 from a variable is so common that in C# you can do it with the –– operator. To decrement the variable count by one, write this statement:

count--;
NOTE
The ++ and – – operators are unary operators, meaning that they take only a single operand. Theyshare the same precedence and left associativity as the ! unary operator, which is discussed in Chapter 4, “Using Decision Statements.”

The following table shows you how to use these two operators.

Don't write this

Write this

 
variable = variable + 1;
 
variable++;
 
variable = variable - 1;
 
variable--;

Prefix and Postfix

The increment (++) and decrement (––) operators are unusual in that you can place them either before or after the variable. Using the operator symbol before the variable is called the prefix form of the operator, and using the operator symbol after the variable is called the postfix form. Here are examples:

count++; // postfix increment 
++count; // prefix increment 
count--; // postfix decrement 
--count; // prefix decrement

Whether you use the prefix or postfix form of the ++ or –– operator makes no difference to the variable being incremented or decremented. For example, if you write count++, the value of count increases by 1, and if you write ++count, the value of count also increases by 1. Knowing this, you're probably wondering why there are two ways to write the same thing. To understand the answer, you must remember that ++ and –– are operators, and that all operators produce a value. The value produced by count++ is the value of count before the increment takes place, whereas the value produced by ++count is the value of count after the increment takes place. Here is an example:

int x; 
x = 42; 
Console.WriteLine(x++); // x is now 43, 42 written out 
x = 42; 
Console.WriteLine(++x); // x is now 43, 43 written out

The way to remember which operand does what is to look at the order of the elements (the operand and the operator) in a prefix or postfix expression. In the expression x++, the variable x occurs first, so its value is used as the value of the expression before x is incremented. In the expression ++x, the operator occurs first, so it is performed before the the value of x is evaluated as the result.

These operators are most commonly used in while and do statements, which will be presented in Chapter 5, “Using Compound Assignment and Iteration Statements.” If you are using the increment and decrement operators in isolation, stick to the postfix form and be consistent.


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