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

ASP.NET Programming with C# and SQL Server

First Edition

Chapter 2Getting Started with

ASP.NET and C#

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 2

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


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 browserASP.NET Programming with C# and SQL Server, First Edition 4

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


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


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 objectASP.NET Programming with C# and SQL Server, First Edition 7

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



• 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 includes five built-in core objects that function at the processing tier (between the client and data storage tiers):– Request– Response– Session– Application– Server


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


Case Sensitivity in ASP.NET

• Like XHTML, C# is case sensitive

• Object names are usually written with initial capitalization– Example: Response.Write()


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 */


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


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


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 sensitiveASP.NET Programming with C# and SQL Server, First Edition 16


Table 2-1 C# keywords


Table 2-2 C# contextual keywords

Naming Variables (cont’d.)

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


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


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 (+)– Example:

Response.Write(“<p>Adult maximum sodium limit is” + mgSodium + “per day.</p>”);


Modifying Variables

• Can change the value of a variable at any point in a program using an assignment statement

• Syntax: variableName = value;


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;


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 declaredASP.NET Programming with C# and SQL Server, First Edition 24

Working with Data Types (cont’d.)


Table 2-3 Commonly used C# primitive data types

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


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


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


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


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



Table 2-4 C# escape sequences

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


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);


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



Figure 2-9 Conceptual example of an array

Storing Data in Arrays (cont’d.)

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];


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– Syntax: arrayName[index] = value;


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


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



Table 2-5 C# operator categories

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



Table 2-6 Arithmetic binary operators

Arithmetic Binary Operators (cont’d.)

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



Table 2-7 Arithmetic unary operators

Arithmetic Unary Operators (cont’d.)


Figure 2-12 Program that uses the prefix increment operator



Figure 2-13 Output of the prefix version of the student ID program



Figure 2-14 Program that uses the postfix increment operator



Figure 2-15 Output of the postfix version of the student ID program


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


Assignment Operators (cont’d.)


Table 2-8 Assignment operators

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



Table 2-9 Comparison operators

Comparison and Conditional Operators (cont’d.)

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


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


Logical Operators (cont’d.)


Table 2-10 Logical operators

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



Table 2-11 C# operator categories


Table 2-11 C# operator categories (cont’d.)

Understanding Operator Precedence (cont’d.)


Figure 2-18 Conceptual illustration of left-to-right associativity

Understanding Operator Precedence (cont’d.)


Figure 2-19 Conceptual illustration of right-to-left associativity

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


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


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


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


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


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