Relational operators compare two values and then return a
Boolean value (true or false). The greater than operator (
>), for example, returns true if the value
on the left of the operator is greater than the value on the right.
5>2 returns the value true,
2>5 returns the value
The relational operators for C# are shown in Table 4-1. This table
assumes two variables:
smallValue, in which
bigValue has been assigned the value 100, and
smallValue the value 50.
Table 4-1. C# relational operators (assumes bigValue = 100 and smallValue = 50)
Given this statement
The expression evaluates to
Greater than or equal to
Less than or equal to
Each of these relational operators acts as you might expect.
Notice that most of these operators are composed of two characters. For
example, the greater than or equal to operator (
>=) is created with the greater than symbol
>) and the equals sign (
=). Notice also that the equals operator is
created with two equals signs (
because the single equals sign alone (
=) is reserved for the assignment
It is not uncommon to confuse the assignment operator (
=) with the equals operator (
==). Just remember that the latter has two
equals signs, and the former only one.
The C# equals operator (
tests for equality between the objects on either side of the operator.
This operator evaluates to a Boolean value (true or false). Thus, the
myX == 5;
evaluates to true if and only if the
myX variable has a value of 5.
As you program, you’ll often want to test whether a
condition is true; for example, using the
if statement, which you’ll see in the next
chapter. Often you will want to test whether two conditions are both
true, only one is true, or neither is true. C# provides a set of
logical operators for this, shown in Table 4-2.
Table 4-2. Logical operators
Given this statement
The expression evaluates to
Both must be true.
Either or both must be true.
Expression must be false.
The examples in this table assume two variables,
x has the value 5 and
y has the value 7.
The and operator tests whether two statements are both true. The first line in Table 4-2 includes an example that illustrates the use of the and operator:
(x == 3) && (y == 7)
The entire expression evaluates false because one side (
x == 3) is false. (Remember that x has the
value 5 and y has the value 7.)
With the or operator, either or both sides must be true; the expression is false only if both sides are false. So, in the case of the example in Table 4-2:
(x == 3) || (y == 7)
the entire expression evaluates true because one side (
y==7) is true.
With a not operator, the statement is true if the expression is false, and vice versa. So, in the accompanying example:
! (x == 3)
the entire expression is true because the tested expression
x==3) is false. (The logic is: “it
is true that it is not true that x is equal to 3.”)
Although most operators are unary (they require one term, such as
myValue++) or binary (they require two
terms, such as
a+b), there is one
ternary operator, which requires three terms: the
conditional operator (
This operator evaluates a conditional expression (an expression that returns a value of type bool) and then invokes either expression1 if the value returned from the conditional expression is true, or expression2 if the value returned is false. The logic is: “if this is true, do the first; otherwise do the second.” Example 4-5 illustrates this concept.
Example 4-5. The ternary operator
The output looks like this:
ValueOne: 10, valueTwo: 20, maxValue: 20
In Example 4-5,
the ternary operator is being used to test whether
valueOne is greater than
valueTwo. If so, the value of
valueOne is assigned to the integer variable
maxValue; otherwise, the value of
valueTwo is assigned to
The compiler must know the order in which to evaluate a series of operators. For example, if I write:
myVariable = 5 + 7 * 3;
there are three operators for the compiler to evaluate (
*). It could, for example, operate
left to right, which would assign the value 5 to
myVariable, then add 7 to the 5 (12) and
multiply by 3 (36)—but of course, then it would throw that 36 away.
This is clearly not what is intended.
The rules of precedence tell the compiler which operators to
evaluate first. As is the case in algebra, multiplication has higher
precedence than addition, so 5+7*3 is equal to 26 rather than 36. Both
addition and multiplication have higher precedence than assignment, so
the compiler will do the math and then assign the result (26) to
myVariable only after the math is
In C#, parentheses are also used to change the order of precedence much as they are in algebra. Thus, you can change the result by writing:
myVariable = (5+7) * 3;
Grouping the elements of the assignment in this way causes the
compiler to add 5+7, multiply the result by 3, and then assign that
value (36) to
Table 4-3. Precedence
The operators are listed in precedence order according to the
category in which they fit. That is, the primary operators (such as
++) are evaluated before the unary
operators (such as
Multiplication is evaluated before addition.
In some complex equations, you might need to nest parentheses to ensure the proper order of operations. For example, assume I want to know how many seconds my family wastes each morning. The adults spend 20 minutes over coffee each morning and 10 minutes reading the newspaper. The children waste 30 minutes dawdling and 10 minutes arguing.
Here’s my algorithm:
(((minDrinkingCoffee + minReadingNewspaper )* numAdults ) + ((minDawdling + minArguing) * numChildren)) * secondsPerMinute.
Although this works, it is hard to read and hard to get right. It’s much easier to use interim variables:
wastedByEachAdult = minDrinkingCoffee + minReadingNewspaper; wastedByAllAdults = wastedByEachAdult * numAdults; wastedByEachKid = minDawdling + minArguing; wastedByAllKids = wastedByEachKid * numChildren; wastedByFamily = wastedByAllAdults + wastedByAllKids; totalSeconds = wastedByFamily * 60;
The latter example uses many more interim variables, but it is far easier to read, understand, and (most importantly) debug. As you step through this program in your debugger, you can see the interim values and make sure they are correct. See Chapter 9 for more information.
 This table includes operators that are so esoteric as to be beyond the scope of this book. For a fuller explanation of each, please see Programming C#, Fourth Edition, by Jesse Liberty (O’Reilly, 2005).