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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Arithmetic Unary Operators (cont’d.) Figure 2-12 Program that uses the prefix increment operator ASP.NET Programming with C# and SQL Server, First Edition

Arithmetic Unary Operators (cont’d.) Figure 2-13 Output of the prefix version of the student ID program ASP.NET Programming with C# and SQL Server, First Edition

Arithmetic Unary Operators (cont’d.) Figure 2-14 Program that uses the postfix increment operator ASP.NET Programming with C# and SQL Server, First Edition

Arithmetic Unary Operators (cont’d.) Figure 2-15 Output of the postfix version of the student ID program ASP.NET Programming with C# and SQL Server, First Edition

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

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

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

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

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

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

Logical Operators (cont’d.) Table 2-10 Logical operators ASP.NET Programming with C# and SQL Server, First Edition

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

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

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

Understanding Operator Precedence (cont’d.) Figure 2-18 Conceptual illustration of left-to-right associativity ASP.NET Programming with C# and SQL Server, First Edition

Understanding Operator Precedence (cont’d.) Figure 2-19 Conceptual illustration of right-to-left associativity ASP.NET Programming with C# and SQL Server, First Edition

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

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

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

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

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