Lecture Windows programming: Chapter 2 - Châu Thị Bảo Hà

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Chapter 2 introduction to the variables - constants – expressions - flow control - methods. In this chapter you will learn: Basic C# syntax variables, constants, expressions; how to branch code, loop code; how to write and call method; how to catch an exception.

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Nội dung Text: Lecture Windows programming: Chapter 2 - Châu Thị Bảo Hà

Chapter 2 Variables - Constants – Expressions Flow control - Methods
What you will learn in this chapter • Basic C# syntax: variables, constants, expressions • How to branch code, loop code • How to write and call method • How to catch an exception 2
Contents 1. Variables - Constants - Expressions 2. More about variables 3. Flow control 4. Methods 5. Using some classes 6. Exception Ebook: from chapter 1 to 6 (Part I) 3
Variables, Constants DataType name; • Declare variable: DataType name = init_value; – example: int x, y; – note: Variables need to be initialized before it’s used const DataType CONST_NAME = value; • Declare constant: – example: const double PI = 3.14; • Data types that are built into C# 4
Primitive Data Types 5
The basic variable naming rules • The first character of a variable name must be either a letter, underscore characters (_) or the at symbol (@) • Subsequent characters may be letters, underscore characters, or numbers • Not use keywords Right variable names: Wrong variable names: • Example: myBigVar 99BottlesOfBeer VAR1 namespace _test It’s-All-Over 6
Naming conventions • The first one, two or three letters of the element's name indicate the type of element; the rest of the name indicates its purpose, and starts with a capital letter – example: iAge, fRate, txtName, btnOK • Names contain multiple words – camelCase • example: phoneNumber, dateOfBirth – PascalCase • example: PhoneNumber, DateOfBirth 7
Example: Using variables class Program { static void Main(string[] args) { int myInteger; string myString; myInteger = 17; myString = "\"myInteger\" is"; Console.WriteLine("{0} {1}.", myString, myInteger); Console.ReadKey(); } } 8
Expression • Expressions are built from operators and operands (variables or literal values) – example: x = 2 * (a + b) • Operators: – mathematical operators: +, -, *, /, % – increment and decrement operators: ++, -- – assignment operators: =, +=, -=, *=, /=, %= – comparison operators: !, &&, || – conditional operators (p.70): Exp1 ? Exp2 : 9
Operator precedence • Example: – var1 = var2 + var3 * var4; – int var1, var2 = 5, var3 = 6; 10
Contents 1. Variables - Constants - Expressions 2. More about variables 3. Flow control 4. Methods 5. Using some classes 6. Exception 11
More about variables • Type conversion – implicit conversion – explicit conversion • Complex variable types – enumerations – structs – arrays • String manipulation 12
Type conversion – Implicit conversion • Implicit conversion (table p.95): var1 = var2; – syntax: – e.g.: Output: ushort i; value of c: a char c = ‘a’; value of i: 97 i = c; Console.WriteLine("value of c: {0}", c); Console.WriteLine("value of i: {0}", i); – bool and string have no implicit conversions – if B=A: any type A whose range of possible values completely ﬁts inside the range 13 of
Type conversion – Explicit conversion [1] • Example: byte byteVar; // 8 bytes short shortVar = 7; // 16 bytes byteVar = shortVar; The C# compiler can detect missing explicit conversions 14
Type conversion – Explicit conversion [2] • Explicit conversion (p.96) (DataType) variable – Syntax: • Example 1: byte byteVar; short shortVar = 7; byteVar = (byte) shortVar; • Example 2: float x = (float)7/2; 15
Type conversion – Explicit conversion [3] • What happens when you try to force a value into a variable into which it won’t ﬁt? – Example: shortVar: byte byteVar; 281 short shortVar = 281; byteVar: 25 byteVar = (byte)shortVar; • How can handle? – [1] check the value of the source variable and compare with the limits of the destination checked() variable unchecked() – 16
Type conversion – Explicit conversion [4] • Example: 17
Explicit conversions using the Convert commands 18
Enumeration (p.102) • An enumeration is a user-defined integer type • Using: should use enum types any time you need to represent a fixed set of constants Using constants: Using enumeration: • Example: final int RED = 1; enum trafficLights final int YELLOW = 2; { final int GREEN = 3; RED, YELLOW, GREEN } 19
Enumeration syntax • Defining enumeration enum { By default, each value is assigned a , corresponding value automatically , according to the order in which it is ... defined, starting from zero. This means that gets the value 0, } gets 1 and so on ; . • Declare variables of enum: • Access value of the enum: 20