Introduction to C#
A computer needs a set of instructions called a program to
perform any operation. A program needs to be written in a specific language
called programming language, so that the computer can understand the
instructions. C# is one such programming language.
This chapter introduces you to C#. it explains how to define
classes and declare variables in C#. In addition, it discusses how to create
the object of a class. Further, it discusses how to write execute C# programs.
Introducing C#
Computer languages have come a long way since the 1940s.during
that period, scientists punched instructions into large, room-sized computer
systems. These instructions were given in machine language, which consisted of
a long series of zeroes and ones. These machine instructions were executed
directly by the CPU. The machine language is called the first generation of
computer language, the assembly language. Assembly language is easier to write
than machine could still understand only machine language. Therefore, the
assembler software was developed to translate the code written in assembly
language into machine language.
In 1967, martin Richard developed a language called BPCL for
writing operating systems. An operating system is a set of program that manages
the resources of a computer and its interactions with users. The era of the
third generation of computer language had arrived. In 1970, ken Thompson teamed
up with Dennis Ritchie and wrote an initial version of the Unix operating
system for a DEC PDP-7 computer.
Dennis Richie was working on a project to further develop
the UNIX operating system. He wanted a low level language, like the assembly
language, that could control hardware efficiently. At the same time, he wanted
the language to provide the features of a high-level language, that is, it
should be able to run on different types of hardware.
B had performance drawbacks, so in 1972 he rewrote B and
called it C. Therefore, C is categorized as both a second and a third
generation language. Thompson and Ritchie rewrote the UNIX operating system in
C. in the years that followed; C was widely accepted and used over different
hardware platforms. This led to many variations of C. in 1989, the American national standards
institute (ANSI), along with the international standards organization (ISO), approved a machine-independent and standard
version of C.
In the early 1980s, Bjarne
Stroustrup up of bell labs developed the C++ language. In his own words,” C++
was designed primarily so that my friends and I would not have to program in
assembly, C, or various modern high-level languages. Its main purpose was to
make writing good programs easier and more pleasant for the individual
programmer.”
C++ was originally known as
‘C with classes’ because two languages contributed to its design: C, which
provided low-level features, and simula67, which provided the class concept.
C++ is an object-oriented language. Other object-oriented language are java,
Smalltalk, and C# (pronounced as C sharp).
Introducing compilers
All language Have a vocabulary, which is a list of words
that have a specific meaning in that language. Language Also have grammar
rules, which state the rules for combining words to form sentences. This
ensures that whatever is spoken in a particular language is understood in the
same way by all people who know the language. Similarly, programming language
also have a vocabulary, which is referred to as of keywords of that language,
and a grammar, which is referred to as the syntax.
Consider a scenario, where one person speaks in English with
the other person. However, the person who is listening understands Chinese and
not English. Therefore, he calls a translator who can translate the words of
English to Chinese. Similarly, computers cannot directly understand the instructions
written in a programming language. Therefore, you need a translator to convert
the instructions written in a programming language to machine language.
A computer is a special that program that processes the
statements written in a particular programming language and converts them into
machine language. Lake everything else in the computer, the compiler also
follows the input-process-output (I-O-P) cycle. It takes the programming
language instructions to convert them to machine language. These instructions
can then be executed by the computer. This process of conversion is called
compilation.
The following figure shows the working of a compiler.
program written in language 2
machine
language program 2
|
Working of a compiler
For each programming language, there is a different compiler
available. For example, to compile a program written in the C language, you
require a C compiler. For a java program, you require a Java Compiler. For C#
program, you will use the CSC compiler.
|
Which
question
Programming
language into machine language.
compiler
|
Using C# for writing programs
Similar to the various programming language, C# also has
some predefined keywords that can be used for writing programs. For example, class is a keyword in C# that is used to
define classes. Keywords are reserved words that have a special meaning.
Further, the syntax for C# defines rules for grammatical arrangement of these
keywords. For example, the syntax of declaring a class in C# is:
Class<class
name>
{
………………
}
In the preceding
syntax, the braces, known as delimiters, are used to indicate the start and end
of a class body.
Classes in C#
C# classes are
the primary building blocks of the language. C# also provides certain
predefined set of classes and methods. These classes and methods provide
various basic functionalities that you may way to implement in your
application.
For example, if
you want to perform some input/output operations in your application, you can
use predefined classes available in the system.
Io namespace
In addition to
using the predefined classes, consider the following code,
Which defines a
classes named Hello:
Public class hello
{
Public static void Main(string
[] args)
{
System. Console. Write Line (“Hello, World!\n”);
}
}
The preceding
class declaration includes the method, main() that will display the message.
“Hello, World!” on your screen. The preceding code includes the following
components:
The class keyword
The class
keyword is used to declare a class. In the preceding code, the class keyword
declares the class, Hello.
The class name
The class
keyword is following by the name of the class. In the preceding code, Hello is
the name of the class defined by using the class keyword.
Class naming conventions in C#
Class name
should follow certain naming conventions or guidelines. A class name:
Should be meaningful (strongly
recommended).
Should ideally be a noun.
Can use either the Pascal case or
Camel case. In Pascal case, the first letter is capitalized and the rest of the
letters are in lower case, such as My class. In camel case, the first letter is
in lower case and the first letter of each subsequent word is capitalized, such
as my class or int Employee Details.
Rules for naming classes in C#
In addition to
the conventions, there are certain rules that must be following while naming
classes in C#. The name of classes:
Ø
Must
begin with a letter. This letter may be followed by a sequence of letters,
digits (0-9), or ‘
Ø
‘_’.
The first character in a class name cannot be a digit.
Ø
Must
not contain an embedded space or a symbol like? -+!@#%^&*()[]{}.,;:”’/and \. However, an
underscore (‘_’) can be used wherever a space is required.
Ø
Must
not use a keyword for a class name. For example, you cannot declare a class
called public.
The main () method
1.
The
first line of code that a C# compiler looks for in the source file is the main
() method. This method is the entry point for an application. This means that
the execution of code starts from the main () method.
2.
The
main () method is ideally used to create objects and invoke the methods of
various classes that constitute the program.
The System. Console. WriteLine ()
Console is a
class that belongs to the system namespace. The console class includes a
predefined Write Line () method. This method display the enclosed text on the
user’s screen. The console class has various other method that are used for
various input/output operations.
The dot
character (.) is used to access the Write Line () method, which is present in
the console class of the System namespace.
The System.
Write Line () statement can also be written as Console. Write Line () if the
statement, using System is included as the first line of the code.
The following code snippet is an example of the
console. Write Line () method:
Console. Write
Line(“Hello, world! \n”);
The preceding
code snippet will display the following message on the screen:
Hello, World!
Escape sequences
To display
special characters, such as the new line character or the backspace character,
you need to include appropriate escape sequences in your code. An escape
sequence is a combination of characters consisting of a backslash (\) followed
by a letter or a combination of digits.
The following
table lists some of the escape sequences provided in C#.
|
Escape sequence
|
Sequence description
|
|
\’
|
Single quotation mark
|
|
\”
|
Double quotation mark
|
|
\\
|
Backslash
|
|
\0
|
NULL
|
|
\a
|
Alert
|
|
\b
|
Backspace
|
|
\n
|
New line
|
|
\r
|
Carriage return
|
|
\t
|
Horizontal tab
|
|
\v
|
Vertical tab
|
The common escape sequences in C#
The following code snippet
depicts the usage of the new line escape sequence:
Console. Write Line
(“Hello \n World”);
The preceding code snippet will
display the following message on the screen:
Hello
World
|
Which question
Identify the output of
the following code snippet:
Console. Write Line
(“Dr\b\b tom Wilkins”);
Dr\b\b tom Wilkins
Dr tom Wilkins
Tom Wilkins
Dr\b tom Wilkins
This ans =(Tom Wilkins)
|
Using variables
|
User
|
|
||||||||||||
Consider a
situation where you have to create a program that accepts two numbers from a
urea and display the sum of the numbers on the screen. New, while reading the
numbers provided by the user, you need to store these numbers somewhere in the
memory so that you can perform the add operation on the numbers. You can store
the numbers in the memory by storing user input in the memory by using
variables.
Using variables to store user input
In the preceding
figure, a user provides 5 and 3 as input. The digit 3 is stored in a variable,
num2. A variable is a location the value. The value could be an integer, such
as ‘L’. A variable is associated with a data type that defines the type of data
that can be stored in the variable.
For example, a
variable called tennis player name will ideally store Characters, whereas a
variable called High score will store numbers. A program refers to a variable
by its name.
For example, a
variable called Tennis Player Name will ideally store characters, whereas a
variable called High_ Score will store number. A program refers to a variable
by name.
The if ….. construct
The if statement in the if ……. Else conditional construct is
followed by a logical expression where data is compared and a decision is made
on the basis of the result of the comparison. The following statements depict
the syntax for the if ……. Else construct:
If (expression)
{
Statements;
}
Else
{
Statements;
}
Consider an example where you have to decide if you want to
have dinner or you want to go to sleep. The condition on which you make a
decision will be your hunger. If you are, you will have dinner; else you will
go to sleep.
The following code snippet shows the decision making of the
preceding example by using the if ….. else construct:
If (hungry==true)
{
Console.WriteLine(“Go and have Dinner!”);
]
Else
{
Console.WriteLine (“ Go to sleep”);
}
The following code shows the use of the if …. Else
construct:
Using System;
Namespace video
{
Class Game
{
Int Age;
Console.WriteLine(“Enter your Age:”);
Age = convert.ToInt32(console.ReadLine());
If (Age<12)
{
Console.WriteLine(“Sorry! This game is for children above 11
years.”);
}
else
{
Console.WriteLine(“play the Game.”);
}
}
}
The preceding code checkswhether the age of the player is
less than 12. The condition in the if statement checks the player, and if the
condition is true, the statements in the else block are executed.
The output of the preceding code will be:
Enter your Age:
14
Play the Game
The else block in the if ……else construct is optional and
can be omitted. The following code snippet shows an example of an if …….. else
construct without the else block:
Int var = 5;
If (var>0)
Console.WriteLine(“var is a positive number.”);
The if …. Else constructs can also be nested inside each
other:
Consider an example where you want to buy a specific model
of Nike shoes. You go to a shoe shop and ask the shopkeeper if shoes of Nike
brand are available. If they have the shoes, you will ask for the model number
that you are looking for. If the requested shoe model is available with them,
then you will buy the shoes; else, you will leave the shop. Therefore, in this
situation you have to make two decisions one after the other. You can take
successive decisions in your program by using the nested if …… else construct.
The following code snippet shows the implementation of the
preceding example by using the nested if ……. Else construct:
If (Nike==available)
If (Mode==M007)
Console.WriteLine(“Buy shoe!”);
Else
Console.WriteLine(“Leave the shop!”);
The following code snippet shows the use of a nested if ……….
Else construct:
Int Number1, Number2, Number3;
Number1 = 10;
Number2 = 20;
Number3 = 30;
If (Number1 > Number2)
{
If (Number1> Number3)
Console.WriteLine(“Number1 is the greatest. ”);
Else
Console.WriteLine(“Number3 is the greatest. ”);
}
Else
{
If (Number2 > Number3)
Console.WriteLine(“Number2 is the greatest.”);
Else
Console.WriteLine(“Number3 is the greatest.”);
}
The preceding code snippet display the greatest of the three
numbers, Number1, Number2, Number3.
The nested if ……. Else construct can be represented by using
logical operators.
The preceding example of the Nike shoe can be changed to an
if ……… else construct by using logical operators. The following code snippet
shows the converting of the nested if …….. else construct to an if ……. Else
construct by using logical operators:
If ((Nike==available)&& (Model==M007))
Console.WriteLine(“Buy shoe!”);
Else
Console.WriteLine(“Leave the shop!”);
The following code snippet shows the use of an if …………else
construct by using logical operators:
Int Number1, Number2, Number3;
Number1 = 10;
Number2 = 20;
Number3 = 30;
If ((Number1> Number2) && (Number2 > Number3))
Console.WriteLine(“Number1 is the greatest”);
In the preceding code snippet, the
Console.WriteLine(“Number1 is the greatest”); statement is executed only if
both the conditions around the && operators evaluate to true.
The
switch….case Construct
Another conditional construct available in C# is the switch
…….. case construct:
Switch (VariableName)
{
Case constantExpression_1:
Statements;
Break;
case Constantexpression_2:
statements;
break;
………….
Case ConstantExpression_n:
Statements;
Break;
Default:
Statements;
Break;
}
When the switch statements is executed, the variable given
in the switch statements is evaluated and compared with each case constant. If
one of the constants is equal to the value of the variable given in the switch
statements, control is passed to the statements following the matched case
statements. The break statements is used to exit the switch statements. This
prevents the execution of the remaining case statements by ending the execution
of the switch ……….. case construct. If none of the cases match, the statements
under the default statements are executed.
The keyword switch following by variable in parentheses, as
shown in the following code snippet:
Switch (var)
Each case keyword is followed by a possible value for the
variable, as shown in the following statement:
Case constantValue:
The data type of the constant should match the data type of
the variable being evaluated by the switch construct. Before entering the
switch construct, a value should be assigned to the switch variable.
You can replace a complex if ………. Else construct with the
switch ……. Case construct when you want to check multiple values for a
variable. The following code snippet is an example of the nested if ……… else
construct:
Int Grade;
Grade = 3;
If (Grade == 1)
Console.WriteLine(“OK”);
Else if (Grade == 2)
Console.WriteLine(“Good”);
Else if (Grade == 3)
Console.WriteLine(“Excellent”);
Else
Console.WriteLine(“Invalid value of Grade”);
The preceding code can be replaced by a simple switch …….
Case construct, as shown in the following code snippet:
Int Grade;
Grade = 500;
Switch (Grade)
{
Case 1:
Console.WriteLine(“OK”);
Break;
Console.WriteLine(“Good”);
Case 3:
Console.WriteLine(“Excellent”);
Break;
Default:
Console.WriteLine(“Invalid value of Grade”);
Break;
}
The switch …….. case construct evaluates an expression only
once at the top of the structure, whereas the if ……… else construct evaluates
the expression for each if statement.
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