C# 0 The Complete Reference

Operator Precedence

Table 4-2 shows the order of precedence for all C# operators, from highest to lowest. This 

table includes several operators that will be discussed later in this book.

Highest

()

[]

.

++

(postfix)

– –

(postfix)

checked

new

sizeof

typeof

unchecked

!

~

(cast)

+

(unar y)

–

(unar y)

++

(prefix)

– –

(prefix)

*

/

%

+

–

<<

>>

<

>

<=

>=

is

==

!=

&

^

|

&&

||

??

?:

=

op

=

=>

Lowest

T

ABLE

 4-2 

The Precedence of the C# Operators

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5

Program Control Statements

T

his chapter discusses C#’s program control statements. There are three categories of 

program control statements: 

selection

 statements, which are the 

if

 and the 

switch

;

iteration

 statements, which consist of the 

for

,

while

,

do-while

, and 

foreach

 loops; and 

jump

 statements, which include 

break

,

continue

,

goto

,

return

, and 

throw

. Except for 

throw

,

which is part of C#’s exception-handling mechanism and is discussed in Chapter 13, the 

others are examined here.

The if Statement

Chapter 2 introduced the 

if

 statement. It is examined in detail here. The complete form of 

the

if

 statement is

if(

condition

)

statement

;

else

statement

;

where the targets of the 

if

 and 

else

 are single statements. The 

else

 clause is optional. The 

targets of both the

 if

 and 

else

 can be blocks of statements. The general form of the 

if

using

blocks of statements is

if(

condition

)

{

statement sequence

}

else

{

statement sequence

}

If the conditional expression is true, the target of the 

if

 will be executed; otherwise, if it 

exists, the target of the 

else

 will be executed. At no time will both of them be executed. 

The conditional expression controlling the 

if

 must produce a 

bool

 result.

Here is a simple example that uses an 

if

 and 

else

 to report if a number is positive or 

negative:

// Determine if a value is positive or negative.

using System;

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CHAPTER

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class PosNeg {

  static void Main() {

    int i;

    for(i=-5; i <= 5; i++) {

      Console.Write("Testing " + i + ": ");

      if(i < 0) Console.WriteLine("negative");

      else Console.WriteLine("positive");

    }

  }

}

The output is shown here:

Testing -5: negative

Testing -4: negative

Testing -3: negative

Testing -2: negative

Testing -1: negative

Testing 0: positive

Testing 1: positive

Testing 2: positive

Testing 3: positive

Testing 4: positive

Testing 5: positive

In this example, if 

i

 is less than zero, then the target of the 

if

 is executed. Otherwise, the 

target of the 

else

 is executed. In no case are both executed.

Nested ifs

A

nested

if

 is an 

if

 statement that is the target of another 

if

 or 

else

. Nested 

if

s are very 

common in programming. The main thing to remember about nested 

if

s in C# is that an 

else

 clause always refers to the nearest 

if

 statement that is within the same block as the 

else

 and not already associated with an

 else

. Here is an example:

if(i == 10) {

  if(j < 20) a = b;

  if(k > 100) c = d;

  else a = c; // this else refers to if(k > 100)

}

else a = d; // this else refers to if(i == 10)

As the comments indicate, the final 

else

 is not associated with 

if(j < 20)

 because it is not 

in the same block (even though it is the nearest 

if

 without an 

else

). Rather, the final 

else

is associated with 

if(i == 10)

. The inner 

else

 refers to 

if(k > 100)

 because it is the closest 

if

within the same block.

The following program demonstrates a nested 

if

. In the positive/negative program 

shown earlier, zero is reported as positive. However, as a general rule, zero is considered 

signless. The following version of the program reports zero as being neither positive nor 

negative.

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PART IPART I

// Determine if a value is positive, negative, or zero.

using System;

class PosNegZero {

  static void Main() {

    int i;

    for(i=-5; i <= 5; i++) {

      Console.Write("Testing " + i + ": ");

      if(i < 0) Console.WriteLine("negative");

      else if(i == 0) Console.WriteLine("no sign");

        else Console.WriteLine("positive");

    }

  }

}

Here is the output:

Testing -5: negative

Testing -4: negative

Testing -3: negative

Testing -2: negative

Testing -1: negative

Testing 0: no sign

Testing 1: positive

Testing 2: positive

Testing 3: positive

Testing 4: positive

Testing 5: positive

The if-else-if Ladder

A common programming construct that is based upon the nested 

if

 is the 

if-else-if

ladder

.

 It 

looks like this:

if(

condition

)

 statement

;

else if(

condition

)

 statement

;

else if(

condition

)

 statement

;

.

.

.

else

statement

;

The conditional expressions are evaluated from the top downward. As soon as a true condition 

is found, the statement associated with it is executed, and the rest of the ladder is bypassed. 

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If none of the conditions is true, then the final 

else

 clause will be executed. The final 

else

often acts as a default condition. That is, if all other conditional tests fail, then the last 

else

clause is executed. If there is no final 

else

 and all other conditions are false, then no action 

will take place.

The following program demonstrates the 

if-else-if

 ladder. It finds the smallest single-

digit factor (other than 1) for a given value.

// Determine smallest single-digit factor.

using System;

class Ladder {

  static void Main() {

    int num;

    for(num = 2; num < 12; num++) {

      if((num % 2) == 0)

        Console.WriteLine("Smallest factor of " + num + " is 2.");

      else if((num % 3) == 0)

        Console.WriteLine("Smallest factor of " + num + " is 3.");

      else if((num % 5) == 0)

        Console.WriteLine("Smallest factor of " + num + " is 5.");

      else if((num % 7) == 0)

        Console.WriteLine("Smallest factor of " + num + " is 7.");

      else

        Console.WriteLine(num + " is not divisible by 2, 3, 5, or 7.");

    }

  }

}

The program produces the following output:

Smallest factor of 2 is 2.

Smallest factor of 3 is 3.

Smallest factor of 4 is 2.

Smallest factor of 5 is 5.

Smallest factor of 6 is 2.

Smallest factor of 7 is 7.

Smallest factor of 8 is 2.

Smallest factor of 9 is 3.

Smallest factor of 10 is 2.

11 is not divisible by 2, 3, 5, or 7.

As you can see, the 

else

 is executed only if none of the preceding 

if

 statements succeeds.

The switch Statement

The second of C#’s selection statements is 

switch

. The 

switch

 provides for a multiway branch. 

Thus, it enables a program to select among several alternatives. Although a series of nested 

if

 statements can perform multiway tests, for many situations the 

switch

 is a more efficient 

approach. It works like this: The value of an expression is successively tested against a list 

of constants. When a match is found, the statement sequence associated with that match is 

executed. The general form of the 

switch

 statement is

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