C# 2008 Programmer's Reference

clear:

int num1 = 5;
int num2 = 5;
int result;
result = num1++;
Console.WriteLine(num1); //---6---
Console.WriteLine(result); //---5---
result = ++num2;
Console.WriteLine(num2); //---6---
Console.WriteLine(result); //---6---

As you can see, if you use the postfix operator (num1++), the value of num1 is assigned to result before the value of num1 is incremented by 1. In contrast, the prefix operator (++num2) first increments the value of num2 by 1 and then assigns the new value of num2 (which is now 6) to result.

Here's another example:

int num1 = 5;
int num2 = 5;
int result;
result = num1++ + ++num2;
Console.WriteLine(num1); //---6---
Console.WriteLine(num2); //---6---
Console.WriteLine(result); //---11---

In this case, both num1 and num2 are initially 5. Because a postfix operator is used on num1, its initial value of 5 is used for adding. And because num2 uses the prefix operator, its value is incremented before adding, hence the value 6 is used for adding. This adds up to 11 (5 + 6). After the first statement, both num1 and num2 would have a value of 6.

Relational Operators

You use relational operators to compare two values and the result of the comparison is a Boolean value — true or false. The following table lists all of the relational operators available in C#.

Operator	Description
==	Equal
!=	Not equal
>	Greater than
>=	Greater than or equal to
<	Lesser than
<=	Lesser than or equal to

The following statements compare the value of num with the numeric 5 using the various relational operators:

int num = 5;
Console.WriteLine(num == 5); //---True---
Console.WriteLine(num != 5); //---False---
Console.WriteLine(num > 5); //---False---
Console.WriteLine(num >= 5); //---True---
Console.WriteLine(num < 5); //---False---
Console.WriteLine(num <= 5); //---True---

A common mistake with the equal relational operator is omitting the second = sign. For example, the following statement prints out the numeric 5 instead of True:

Console.WriteLine(num = 5);

A single = is the assignment operator.

C programmers often make the following mistake of using a single = for testing equality of two numbers:

if (num = 5) //---use == for testing equality---
{
Console.WriteLine('num is 5');
}

Fortunately, the C# compiler will check for this mistake and issue a 'Cannot implicitly convert type 'int' to 'bool'' error.

Logical Operators

C# supports the use of logical operators so that you can evaluate multiple expressions. The following table lists the logical operators supported in C#.

Operator	Description
&&