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Category Operators Description Associativity Unary ! + - ++ -- Multiplicative * / % Additive + - Relational < >= Equality == != Logical NOT Returns the value of the operand unchanged Returns the value of the operand negated Pre-increment Pre-decrement Multiply Divide Division remainder (modulus) Addition Subtraction Less than Less than or equal to Greater than Greater than or equal to Equal to Not equal to Left Left Left Left Left Conditional AND && Conditional AND Left Conditional OR || Conditional OR Left Assignment = Assigns the right-hand operand to the left and returns the value that was assigned Right Notice that the && operator and the || operator have a different precedence: && is higher than ||. Using if statements to make decisions In a method, when you want to choose between executing two different statements depending on the result of a Boolean expression, you can use an if statement. Understanding if statement syntax The syntax of an if statement is as follows (if and else are C# keywords): if ( booleanExpression ) statement-1; else statement-2; If booleanExpression evaluates to true, statement-1 runs; otherwise, statement-2 runs. The else keyword and the subsequent statement-2 are optional. If there is no else clause and the booleanExpression is false, execution continues with whatever code follows the if statement. Also, CHAPTER 4 Using decision statements 91
notice that the Boolean expression must be enclosed in parentheses; otherwise, the code will not compile. For example, here’s an if statement that increments a variable representing the second hand of a stopwatch. (Minutes are ignored for now.) If the value of the seconds variable is 59, it is reset to 0; otherwise, it is incremented by using the ++ operator: int seconds; ... if (seconds == 59) seconds = 0; else seconds++; Boolean expressions only, please! The expression in an if statement must be enclosed in parentheses. Additionally, the expression must be a Boolean expression. In some other languages—notably C and C++—you can write an integer expression, and the compiler will silently convert the integer value to true (nonzero) or false (0). C# does not support this behavior, and the compiler reports an error if you write such an expression. If you accidentally specify the assignment operator (=) instead of the equality test operator (==) in an if statement, the C# compiler recognizes your mistake and refuses to compile your code, such as in the following example: int seconds; ... if (seconds = 59) // compile-time error ... if (seconds == 59) // ok Accidental assignments were another common source of bugs in C and C++ programs, which would silently convert the value assigned (59) to a Boolean expression (with anything nonzero considered to be true), with the result being that the code following the if statement would be performed every time. Incidentally, you can use a Boolean variable as the expression for an if statement, although it must still be enclosed in parentheses, as shown in this example: bool inWord; ... if (inWord == true) // ok, but not commonly used ... if (inWord) // more common and considered better style 92 PART I Introducing Microsoft Visual C# and Microsoft Visual Studio 2015
Page 1 and 2: Microsoft Visual C# Step by Step Ei
Page 3 and 4: PUBLISHED BY Microsoft Press A Divi
Page 5 and 6: PART IV BUILDING UNIVERSAL WINDOWS
Page 7 and 8: Associativity and the assignment op
Page 9 and 10: Summary. . . . . . . . . . . . . .
Page 11 and 12: Using multidimensional arrays . . .
Page 13 and 14: Using properties . . . . . . . . .
Page 15 and 16: Summary. . . . . . . . . . . . . .
Page 17 and 18: Canceling tasks and handling except
Page 20 and 21: Introduction Microsoft Visual C# is
Page 22 and 23: ■ ■ Part III, “Defining exten
Page 24 and 25: System requirements You will need t
Page 26 and 27: For those of you who like to know a
Page 28 and 29: Project/Solution Description Chapte
Page 30 and 31: Project/Solution Description Chapte
Page 32: We want to hear from you At Microso
Page 35 and 36: Note The answers to these questions
Page 37: The outcome of the || operator is t
Page 41 and 42: Cascading if statements You can nes
Page 43 and 44: private void compareClick(object se
Page 45 and 46: else if (leftHandSide.Day > rightHa
Page 47 and 48: Understanding switch statement synt
Page 49 and 50: in a switch statement (even the def
Page 51 and 52: If the current character being copi
Page 54 and 55: Index Symbols & (ampersand) & (AND)
Page 56 and 57: inary operators creating, 232-241 d
Page 58 and 59: code CanExecuteChanged events, 670,
Page 60 and 61: CountdownEvent class concurrent ope
Page 62 and 63: Ellipse class for structures, 209 w
Page 64 and 65: forms exception objects, 144 except
Page 66 and 67: indexers H handheld devices. See Un
Page 68 and 69: lock statements I/O operations asyn
Page 70 and 71: Name property invoking through dele
Page 72 and 73: Parallel.Invoke method okClick meth
Page 74 and 75: eference types number of, 521 Progr
Page 76 and 77: static properties security, unsafe
Page 78 and 79: throughput, improving System.String
Page 80 and 81: views voice activation, 680-695 Win
Page 82: yield keyword blocking current thre

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