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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Case Sensitivity in ASP.NET
• Like XHTML, C# is case sensitive
• Object names are usually written with initial
capitalization
– Example: Response.Write()
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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 */
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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
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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
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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
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Table 2-1 C# keywords
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Naming Variables (cont’d.)
Table 2-2 C# contextual keywords
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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
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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
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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>”);
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Modifying Variables
• Can change the value of a variable at any point in a
program using an assignment statement
• Syntax: variableName = value;
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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;
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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
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Working with Data Types (cont’d.)
Table 2-3 Commonly used C# primitive data types
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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
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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
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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
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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
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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
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Table 2-4 C# escape sequences
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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
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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);
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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
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Storing Data in Arrays (cont’d.)
Figure 2-9 Conceptual example of an array
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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];
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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;
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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
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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
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Table 2-5 C# operator categories
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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
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Arithmetic Binary Operators (cont’d.)
Table 2-6 Arithmetic binary operators
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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
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Arithmetic Unary Operators (cont’d.)
Table 2-7 Arithmetic unary operators
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Arithmetic Unary Operators (cont’d.)
Figure 2-12 Program that uses the prefix increment operator
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Arithmetic Unary Operators (cont’d.)
Figure 2-13 Output of the prefix version of the student ID program
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Arithmetic Unary Operators (cont’d.)
Figure 2-14 Program that uses the postfix increment operator
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Arithmetic Unary Operators (cont’d.)
Figure 2-15 Output of the postfix version of the student ID program
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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
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Assignment Operators (cont’d.)
Table 2-8 Assignment operators
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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
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Comparison and Conditional
Operators (cont’d.)
Table 2-9 Comparison operators
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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
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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
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Logical Operators (cont’d.)
Table 2-10 Logical operators
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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
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Table 2-11 C# operator categories
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Table 2-11 C# operator categories (cont’d.)
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Understanding Operator Precedence
(cont’d.)
Figure 2-18 Conceptual illustration of left-to-right associativity
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Understanding Operator Precedence
(cont’d.)
Figure 2-19 Conceptual illustration of right-to-left associativity
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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
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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
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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
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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
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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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