C# 0 The Complete Reference

byte

 is needed when assigning 

b * b

 back to 

b

! The 

reason is because in 

b * b

, the value of 

b

 is promoted to 

int

 when the expression is evaluated. 

Thus,

b * b 

results in an 

int

 value, which cannot be assigned to a 

byte

 variable without a 

cast. Keep this in mind if you get unexpected type-incompatibility error messages on 

expressions that would otherwise seem perfectly correct.

This same sort of situation also occurs when performing operations on 

char

s. For 

example, in the following fragment, the cast back to 

char

 is needed because of the 

promotion of 

ch1

 and 

ch2

 to 

int

 within the expression

char ch1 = 'a', ch2 = 'b';

ch1 = (char) (ch1 + ch2);

Without the cast, the result of adding 

ch1

 to 

ch2

 would be 

int

, which can’t be assigned to 

a

char

.

Type promotions also occur when a unary operation, such as the unary 

–

, takes place. 

For the unary operations, operands smaller than 

int

 (

byte

,

sbyte

,

short

, and 

ushort

) are 

promoted to 

int

. Also, a 

char

 operand is converted to 

int

. Furthermore, if a 

uint

 value is 

negated, it is promoted to 

long

.

Using Casts in Expressions

A cast can be applied to a specific portion of a larger expression. This gives you fine-grained 

control over the way type conversions occur when an expression is evaluated. For example, 

consider the following program. It displays the square roots of the numbers from 1 to 10. It 

also displays the whole number portion and the fractional part of each result, separately. To 

do so, it uses a cast to convert the result of 

Math.Sqrt( )

 to 

int

.

// Using casts in an expression.

using System;

class CastExpr {

  static void Main() {

    double n;

     for(n = 1.0; n <= 10; n++) {

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