1. ASP.NET Programming with C# and SQL Server First Edition
Chapter 2
Getting Started with ASP.NET and C#

2. Objectives In this chapter, you will: Create basic ASP.NET Web pages
Work with variables, constants, and data types
Use expressions and operators
Learn about operator precedence
ASP.NET Programming with C# and SQL Server, First Edition

3. Introduction
The ability to store values in computer memory and manipulate those values is one of the most important aspects of programming
Variables: values stored in computer memory
Data types: categories used to classify the values, or data, stored in variables
ASP.NET Programming with C# and SQL Server, First Edition

4. Creating Basic ASP.NET Web Pages
ASP.NET pages have a file extension of .aspx
ASP.NET pages can also contain HTML and XHTML elements
All .aspx documents are sent by the Web server to the scripting engine for processing
Non-ASP.NET code is ignored by the scripting engine
Web server returns the results of the ASP.NET program along with the HTML or XHTML to the client’s browser
ASP.NET code is never sent to the browser
ASP.NET Programming with C# and SQL Server, First Edition

5. Creating ASP.NET Code Render Blocks
Code render blocks: define inline code or inline expressions that execute when a Web page renders
Inline code: one or more lines of code (or statements) contained within a code render block
Delimiter: a character or sequence of characters used to mark the beginning and end of a code segment
Use <% and %> to designate inline code
Scripting commands are placed within the delimiters
ASP.NET Programming with C# and SQL Server, First Edition

6. Creating ASP.NET Code Render Blocks (cont’d.)
C# commands end with a semicolon (;)
ASP processing directive: provides information on how to process the code
Use and %> delimiters
@Page processing directive: uses the Language attribute to identify the language that will be used in the ASP.NET page
Inline expression: scripting code expression used within an ASP.NET page
Use <%= and %> delimiters
ASP.NET Programming with C# and SQL Server, First Edition

7. Understanding Classes and Objects
Object-oriented programming (OOP): refers to the creation of reusable software objects that can be incorporated into other programs
Object: programming code and data that can be treated as an individual unit or component
Class: a template, or blueprint, from which you create new objects
Instance: an object that has been created from an existing class
When you create an object from a class, you are instantiating the object
ASP.NET Programming with C# and SQL Server, First Edition

8. Understanding Classes and Objects (cont’d.)
Procedure: a logical unit containing a group of individual statements
Method: a procedure associated with a class
Property: a piece of data associated with an object
A class’s methods, properties, and other types of elements are called its members
To use an object and its method, type the object name, followed by a period, and then the method name
ASP.NET Programming with C# and SQL Server, First Edition

9. Understanding Classes and Objects (cont’d.)
Argument: specific information provided to a method
Passing arguments: the process of providing an argument to a method
Text string (or literal string): text contained within double quotation marks
Empty string: a zero-length string value
To use an object’s property, type the object name, followed by a period, and then the property name
Properties are only used to store data
ASP.NET Programming with C# and SQL Server, First Edition

10. Understanding Classes and Objects (cont’d.)
ASP.NET includes five built-in core objects that function at the processing tier (between the client and data storage tiers):
Request
Response
Session
Application
Server
ASP.NET Programming with C# and SQL Server, First Edition

11. Displaying Program Results
Response object: represents the information that will be sent back to the client
Write() method: a method of the Response object that is used to add new text to a Web page while it is being rendered
Requires a text string as an argument
Can include HTML elements as part of the argument
ASP.NET Programming with C# and SQL Server, First Edition

12. Case Sensitivity in ASP.NET
Like XHTML, C# is case sensitive
Object names are usually written with initial capitalization
Example: Response.Write()
ASP.NET Programming with C# and SQL Server, First Edition

13. Adding Comments to an ASP.NET Program
Comments: nonprinting lines placed in code to contain remarks for programmers
It is good programming practice to include comments in your code
C# supports two kinds of comments:
Line comment: hides a single line of code by prefacing the line with //
Block comment: hides multiple lines of code by enclosing the block in /* and */
ASP.NET Programming with C# and SQL Server, First Edition

14. Adding Comments to an ASP.NET Program (cont’d.)
Server-side comments:
Can be used anywhere except in code render or code declaration blocks
Are not processed on the server and do not display on the rendered page
Use <%-- and --%> delimiters
ASP.NET Programming with C# and SQL Server, First Edition

15. Using C# Variables and Constants
Variables: values a program stores in computer memory
Specific locations in the computer’s memory
Must first create the variable and assign it a name
“Assigning a value to a variable” means storing a value in it
A variable may contain different values at different times while the program is running
ASP.NET Programming with C# and SQL Server, First Edition

16. Naming Variables Identifier: the name assigned to a variable
Must begin with upper or lowercase ASCII letter or underscore, followed by letters, numbers, or underscores
Cannot use spaces
Cannot use keywords for identifiers
Keywords (or reserved words): special words that are part of the C# language syntax
Contextual keywords: have special meaning in C# but are not reserved as keywords
Variable names are case sensitive
ASP.NET Programming with C# and SQL Server, First Edition

17. Table 2-1 C# keywords
ASP.NET Programming with C# and SQL Server, First Edition

18. Naming Variables (cont’d.)
Table 2-2 C# contextual keywords
ASP.NET Programming with C# and SQL Server, First Edition

19. Creating Variables
Must create (declare) a variable before you can use it by specifying its data type and its name
Syntax: type variableName;
Integer data type: stores positive or negative numbers with no decimal places, or the value 0
Can assign a value to a variable (initialize it) when declaring it
Syntax: type variableName = value;
Assignment operator (=): assigns the value on the right side of the expression to the variable on the left side
ASP.NET Programming with C# and SQL Server, First Edition

20. Creating Variables (cont’d.)
The value assigned to a variable must have the same data type as the variable
Literal values (or literals): the values assigned to integer variables or other numeric variables
An error will occur if you try to use a variable that has not been assigned a value when declared or before it has been used in the program
ASP.NET Programming with C# and SQL Server, First Edition

21. Displaying Variables
To print a variable, pass the variable name to the Response.Write() method
Syntax: Response.Write(variableName)
Example:
int mgSodium = 2300;
Response.Write(mgSodium);
Can combine text strings with variables, separated with the plus sign (+)
Response.Write(“<p>Adult maximum sodium limit is” + mgSodium + “per day.</p>”);
ASP.NET Programming with C# and SQL Server, First Edition

22. Modifying Variables
Can change the value of a variable at any point in a program using an assignment statement
Syntax: variableName = value;
ASP.NET Programming with C# and SQL Server, First Edition

23. Creating Constants
Constant: contains information that does not change during the program execution
Constant naming rules are the same as those for variables
Use the const keyword before the data type when declaring a constant
Constants must be initialized in the declaration statement and cannot be changed later
Syntax: const type constantName = initialValue;
ASP.NET Programming with C# and SQL Server, First Edition

24. Working with Data Types
Data type: the specific category of information that a variable contains
Data type is used to determine the amount of memory needed to store the variable’s value
Primitive types: data types that can be assigned only a single value
Strongly typed programming languages: languages that require the declaration of data type for variables
Also known as static typing because the data type does not change after it is declared
ASP.NET Programming with C# and SQL Server, First Edition

25. Working with Data Types (cont’d.)
Table 2-3 Commonly used C# primitive data types
ASP.NET Programming with C# and SQL Server, First Edition

26. Working with Data Types (cont’d.)
Loosely typed programming languages: languages that do not require the declaration of data types for variables
Also known as dynamic typing, because data types can change after declaration
C# is a strongly typed programming language
ASP.NET Programming with C# and SQL Server, First Edition

27. Using Numeric Data Types
Integer: a positive or negative whole number with no decimal places
Use int or long data types
Floating-point number: a number with decimal places or a number written in exponential notation
Use float, double, and decimal data types
Exponential notation (scientific notation): shortened format for writing very large numbers or numbers with many decimal places
Literal floating-point values are treated as type double by C# when used in assignment statements
ASP.NET Programming with C# and SQL Server, First Edition

28. Working with Boolean Values
Boolean value: a logical value of true or false
Used for making decisions in a program
Can only use the values true and false in C#
Use the keyword bool when declaring a Boolean variable
Syntax: bool variableName = value
ASP.NET Programming with C# and SQL Server, First Edition

29. Using the Char Data Type
char data type: stores any single character or escaped hexadecimal Unicode character in single quotations
Example: char semesterGrade = ‘B’;
Unicode: a standardized set of characters from many of the world’s languages
Hexadecimal: a numeral system based on the value of 16
Uses 16 characters: 0-9 plus A through F
Hexadecimal values must be preceded by the \u escape sequence and enclosed in single quotations
ASP.NET Programming with C# and SQL Server, First Edition

30. Using the String Data Type
string data type: used to store text string variables
Literal values must be enclosed in double quotations
Syntax: string variableName = “value”;
Escape character: tells the compiler or interpreter that the following character has a special purpose
In C#, the escape character is the backslash \
Escape sequence: the escape character combined with other characters
Used to insert a special character into a string
ASP.NET Programming with C# and SQL Server, First Edition

31. Table 2-4 C# escape sequences
ASP.NET Programming with C# and SQL Server, First Edition

32. Casting Types
You cannot change the data type of a variable while the program is running
To use the contents of a variable as a different data type, you must cast the variable to a new data type
Casting (or type casting): copies variable’s value; converts it to store it into a variable of another type
Syntax: newVariable = (newType) oldVariable
If you do not cast a variable to another data type, C# tries to automatically cast it, provided the target value is able to store a value of the specified size
ASP.NET Programming with C# and SQL Server, First Edition

33. Casting Types (cont’d.)
Can also use methods of the Convert class to manually convert variables to other data types
ToString() method: converts a variable to a string data type
Pass the name of the variable to be converted into the method of the Convert class
Syntax: Convert.ToString(variableName);
ASP.NET Programming with C# and SQL Server, First Edition

34. Storing Data in Arrays
Array: set of data represented by a single variable name
Can be thought of as a collection of variables stored within a single variable
All of the data must be of the same data type
ASP.NET Programming with C# and SQL Server, First Edition

35. Storing Data in Arrays (cont’d.)
Figure 2-9 Conceptual example of an array
ASP.NET Programming with C# and SQL Server, First Edition

36. Declaring and Initializing Arrays
Element: each piece of data stored within an array
Index: an element’s numeric position within the array
Index is enclosed in square brackets when referring to an element
Syntax: arrayName[index]
Must declare an array’s data type and number of elements
Syntax: type[] arrayName = new type[elements];
ASP.NET Programming with C# and SQL Server, First Edition

37. Declaring and Initializing Arrays (cont’d.)‏
To assign a value to an individual array element, include the index for the element
Syntax: arrayName[index] = value;
To access an element’s value, include the element’s index
Example: Response.Write(arrayName[index]);
To modify an element’s value, include the index for the element
ASP.NET Programming with C# and SQL Server, First Edition

38. Determining the Number of Elements in an Array
Length property: returns the number of elements in an array
Syntax: arrayName.Length
Note that property names are not followed by parentheses, as method names are
ASP.NET Programming with C# and SQL Server, First Edition

39. Building Expressions
Expression: a combination of literal values, variables, operators, and other expressions that can be evaluated to produce a result
Operands: variables and literals contained in an expression
Operators: symbols used in expressions to manipulate operands
Binary operator: requires an operand before and after the operator
Unary operator: requires a single operator either before or after the operator
ASP.NET Programming with C# and SQL Server, First Edition

40. Table 2-5 C# operator categories
ASP.NET Programming with C# and SQL Server, First Edition

41. Arithmetic Binary Operators
Arithmetic binary operators: used to perform mathematical calculations, including addition, subtraction, multiplication, division, and modulus
Modulus: divides one operand by another and returns only the remainder
The C# interpreter does not convert strings to numbers when using the addition operator
The strings are combined together
ASP.NET Programming with C# and SQL Server, First Edition

42. Arithmetic Binary Operators (cont’d.)
Table 2-6 Arithmetic binary operators
ASP.NET Programming with C# and SQL Server, First Edition

43. Arithmetic Unary Operators
Arithmetic unary operators: allow you to perform arithmetic operations on a single variable
Prefix operator: placed before a variable
Value of the operand is returned after the operator is applied to it
Postfix operator: placed after a variable
Value of the operand is returned before the operator is applied to it
ASP.NET Programming with C# and SQL Server, First Edition

44. Arithmetic Unary Operators (cont’d.)
Table 2-7 Arithmetic unary operators
ASP.NET Programming with C# and SQL Server, First Edition

45. Arithmetic Unary Operators (cont’d.)
Figure Program that uses the prefix increment operator
ASP.NET Programming with C# and SQL Server, First Edition

46. Arithmetic Unary Operators (cont’d.)
Figure Output of the prefix version of the student ID program
ASP.NET Programming with C# and SQL Server, First Edition

47. Arithmetic Unary Operators (cont’d.)
Figure Program that uses the postfix increment operator
ASP.NET Programming with C# and SQL Server, First Edition

48. Arithmetic Unary Operators (cont’d.)
Figure Output of the postfix version of the student ID program
ASP.NET Programming with C# and SQL Server, First Edition

49. Assignment Operators
Assignment operators: used to assign a value to a variable
Compound assignment operators: perform mathematical calculations on variables and literal values in an expression, and then assign a new value to the left operand
Concatenation operator (+): used to combine two strings
ASP.NET Programming with C# and SQL Server, First Edition

50. Assignment Operators (cont’d.)
Table 2-8 Assignment operators
ASP.NET Programming with C# and SQL Server, First Edition

51. Comparison and Conditional Operators
Comparison operators: used to compare two operands and determine if one numeric value is greater than another
Return a Boolean value of true or false
Values being compared must be of the same data type
Nonnumeric values are compared by their hexadecimal Unicode values
Lowercase letters have higher hexadecimal values than their corresponding uppercase letters
ASP.NET Programming with C# and SQL Server, First Edition

52. Comparison and Conditional Operators (cont’d.)
Table 2-9 Comparison operators
ASP.NET Programming with C# and SQL Server, First Edition

53. Comparison and Conditional Operators (cont’d.)
Conditional operator: returns one of two results, based on the results of a conditional expression
Syntax: conditional expression? result1: result2;
If the conditional expression evaluates to true, result1 is used; otherwise, result2 is used
ASP.NET Programming with C# and SQL Server, First Edition

54. Logical Operators
Logical operators: used for comparing two Boolean operands for equality
Or (||) and And (&&): binary operators requiring two operands
Not (!): unary operator requiring a single operand
ASP.NET Programming with C# and SQL Server, First Edition

55. Logical Operators (cont’d.)
Table Logical operators
ASP.NET Programming with C# and SQL Server, First Edition

56. Understanding Operator Precedence
Operator precedence: refers to the order in which operations in an expression are evaluated
Operators in a higher grouping have precedence over operators in a lower grouping
Operators in the same grouping have the same order of precedence
Evaluated from left to right or right to left, depending on the operators involved
Associativity: order in which operators of equal precedence execute
ASP.NET Programming with C# and SQL Server, First Edition

57. Table 2-11 C# operator categories
ASP.NET Programming with C# and SQL Server, First Edition

58. Table 2-11 C# operator categories (cont’d.)
ASP.NET Programming with C# and SQL Server, First Edition

59. Understanding Operator Precedence (cont’d.)
Figure Conceptual illustration of left-to-right associativity
ASP.NET Programming with C# and SQL Server, First Edition

60. Understanding Operator Precedence (cont’d.)
Figure Conceptual illustration of right-to-left associativity
ASP.NET Programming with C# and SQL Server, First Edition

61. Summary
Code render blocks define inline code or inline expressions that execute when a Web page renders
Use an ASP processing directive to declare the language that ASP.NET will use
Object-oriented programming (OOP): refers to the creation of reusable software objects
Comments: nonprinting lines placed in code
Variables: values stored in computer memory
Identifier is a name assigned to a variable
ASP.NET Programming with C# and SQL Server, First Edition

62. Summary (cont’d.)‏
Keywords (reserved words): special words that are part of the C# language syntax
Constant: contains information that does not change during the program execution
Data type: category of information that a variable contains
C# is a strongly typed programming language
Integer: positive or negative number with no decimal places
ASP.NET Programming with C# and SQL Server, First Edition

63. Summary (cont’d.)‏
Floating-point number: number with decimal places or that is written in exponential notation
Boolean value is a logical value of true or false
char data type stores any single character
string data type stores text string variables
Casting (type casting): copies the value of one variable into a variable of another data type
Array: contains a set of data represented by a single variable name
ASP.NET Programming with C# and SQL Server, First Edition

64. Summary (cont’d.)
Expression: combination of literal values, variables, operators, and other expressions that can be evaluated by the C# interpreter to produce a result
Arithmetic operators: used to perform mathematical calculations
Assignment operators: assign values to variables
Comparison operators: used to compare two operands
Conditional operator: returns one of two results, based on the results of a conditional expression
ASP.NET Programming with C# and SQL Server, First Edition

65. Summary (cont’d.)
Logical operators: used for comparing two Boolean operands for equality
Operator precedence: refers to the order in which operations in an expression are evaluated
Order of precedence for operators in the same precedence group is determined by the operator’s associativity
ASP.NET Programming with C# and SQL Server, First Edition