Chapter One

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18 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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1

Chapter One

A First Program Using
C#

2

Objectives


Learn about programming tasks


Learn object
-
oriented programming concepts


Learn about the C# programming language


Learn how to write a C# program that
produces output


Learn how to select identifiers to use within
your programs


3

Objective


Learn how to compile and execute a C#
program from the command line


Learn how to add comments to a C# program


Learn how to compile and execute a program
using Visual Studio IDE


Learn how to eliminate the reference to Out by
using the System namespace

4

Programming


A computer
program
is a set of instructions that you
write to tell a computer what to do


Programmers do not use
machine language

when
creating computer programs. Instead, programmers tend
to use
high
-
level programming languages


Each high
-
level language has its own
syntax

and limited
set of vocabulary that is translated into machine code by
a
compiler


In addition to understanding syntax, a programmer must
also understand programming
logic

5

Object
-
Oriented Programming


Variables

are named computer memory locations used
to hold values that may vary


Operations

are usually
called
or
invoked

to manipulate
variables


A
procedural program

defines the variable memory
locations, then calls a series of procedures to input,
manipulate, and output the value stored in those
locations


A single procedural program often contains hundreds of
variables and thousands of procedure calls

6

Object
-
Oriented Programming


Object
-
oriented

programming is an extension of
procedural programming, which in addition to variables
and procedures contains: objects, classes,
encapsulation, interfaces, polymorphism, and inheritance


Objects

are object
-
oriented components


Attributes

of an object represent its characteristics


A
class

is a category of objects or a type of object


An
instance

refers to an object based on a class

7

Object
-
Oriented Programming


For example:


An Automobile is a class whose objects have the following
attributes: year, make, model, color, and current running status


Your 1997 red Chevrolet is an instance of the class that is made
up of all Automobiles


Methods

of classes are used to change attributes and
discover values of attributes


The Automobile class may have the following methods:
getGas(), accelerate(), applyBreaks()

8

Object
-
Oriented Programming


Methods and variables in object
-
oriented programming
are
encapsulated,
that is, users are only required to
understand the
interface

and not the internal workings
of the class


Polymorphism
and
Inheritance
are two distinguishing
features in the object
-
oriented programming approach


Polymorphism describes the ability to create methods
that act appropriately depending on the context


Inheritance provides the ability to extend a class so as to
create a more specific class

9

The C# Programming Language


C# was developed as an object
-
oriented and
component
-
oriented language


It exists as part of the
Visual Studio .NET

package


C# (like Java) is modeled after the C++ programming
language


Pointers are not used in C#


C# does NOT require the use of object destructors,
forward declarations, or #include files


It has the ability to pass by reference


Multiple inheritance is not allowed in C#

10

Writing a C# Program that Produces Output


“This is my first C# program” is a
literal string

of
characters


The string appears in parenthesis because it is a
parameter

or an

argument


The
WriteLine()

method prints a line of output on the
screen

11

Writing a C# Program that Produces Output


Out

is an object that represents the screen


The Out object was created and endowed with the
method WriteLine()


Not all objects have the WriteLine() method

12

Writing a C# Program that Produces Output


Console
is a class


Console defines the attributes of a collection of similar
“Console” objects

13

Writing a C# Program that Produces Output


System

is a
namespace
, which is a scheme that
provides a way to group similar classes


Namespaces are used to organize classes

14

Writing a C# Program that Produces Output


The difference between the above code and the previous
code is the amount of
whitespace


Both versions of code share the same method header
(including access modifiers and other keywords)

15

Selecting Identifiers


Every method used in C# must be part of a class


A C# class name or
identifier

must meet the basic
following requirements:


An identifier must begin with an underscore or a letter


An identifier can contain only letters or digits, not special
characters such as #,$, or &


An identifier cannot be a C# reserved keyword

16

Selecting Identifiers


The reserved
public

keyword is an
access modifier

that defines the circumstance under which a class can
be accessed

17

Writing a C# Program that Produces Output


Code written for a C# program using a text editor

18

Compiling and Executing a Program from
the Command Line


After creating
source code
, you must do the following
before you can view the program output:


Compile the source code into
intermediate language
(IL)


Use the C#
just in time (JIT)

compiler to translate the
intermediate code into executable statements


19

Compiling and Executing a Program from
the Command Line


After compiling your source code (typing
csc

followed by
the
filename
), you will have three possible outcomes:


You receive an operating system error message


You receive one or more program language error
messages


You receive no error messages, indicating that the
program has compiled successfully

20

Compiling and Executing a Program from
the Command Line


If you receive an operating system message it may
mean that:


You misspelled the command csc


You misspelled the filename


You forgot to include the extensions .cs with the
filename


You didn’t use the correct case


You are not within the correct subdirectory or folder
on your command line


The C# compiler was not installed properly


You need to set a path command



21

Compiling and Executing a Program from
the Command Line


A
syntax error

occurs when you introduce typing errors
into your program


The C# compiler issues
warnings

as wells as errors


If a syntax error occurs, you must reopen the source
code and make the necessary corrections


If you compile the program with no errors (using
csc
file.cs
) you can run the program from the command
prompt by typing the name of the .
exe

file created

22

Compiling and Executing a Program from
the Command Line


Output of Hello Program

23

Adding Comments to a Program


In large programs it becomes difficult to remember why
certain steps were included and the role of certain
variables and methods


Program comments

are nonexecuting statements that
you add to document a program


You can also
comment out

various statements in a
program to debug and observe the effects of the
program with the statement or statements commented
out

24

Adding Comments to a Program


There are three types of comments in C#:


Line comments


Block comments


XML
-
documentation format

25

Compiling and Executing a Program Using
the Visual Studio IDE


C# programs can also be written using the Visual Studio
IDE (instead of a text editor). This approach offers many
advantages including:


Some of the code you need is already created for you


The code is displayed in color, so you can more easily identify
parts of your program


If error messages appear when you compile your program, you
can double
-
click on an error message and the cursor will move
to the line of code that contains the error


Other debugging tools are available


26

Compiling and Executing a Program Using
the Visual Studio IDE


Navigating to Visual Studio .NET

27

Compiling and Executing a Program Using
the Visual Studio IDE


Creating a project

28

Compiling and Executing a Program Using
the Visual Studio IDE


Selecting project options

29

Compiling and Executing a Program Using
the Visual Studio IDE


The console application template

30

Compiling and Executing a Program Using
the Visual Studio IDE


Output screen after compiling the Hello program

31

Compiling and Executing a Program Using
the Visual Studio IDE


Output of the Hello program as run from the Visual
Studio IDE

32

Compiling and Executing a Program Using
the Visual Studio IDE


List of Hello Program Files

33

Eliminating the Reference to Out by Using
the System Namespace


A program may contain an unlimited number of
statements, as long as they are each terminated by a
semicolon

34

Eliminating the Reference to Out by Using
the System Namespace


The Output of ThreeLines program

35

Eliminating the Reference to Out by Using
the System Namespace


When you need to repeatedly use a class from the same
namespace, you can shorten statements by using the

using
” keyword


Output is identical as the previous version of ThreeLines

36

Eliminating the Reference to Out by Using
the System Namespace


An
alias

is an alternative name for a class


An alias can be used to shorten a long class name (as in
the above example)

37

Chapter Summary


A computer program is a set of instructions that you write
to tell a computer what to do


Procedural Programming involves creating computer
memory locations, called variables, and a set of
operations, called procedures. In object
-
oriented
programming, you envision program components as
objects that are similar to concrete objects in the real
world


The C# language was developed as an object
-
oriented
and component
-
oriented language

38

Chapter Summary


To write a C# program that produces a line of console
output, you must pass a literal string as a parameter to
the System.Console.Out.WriteLine() method


You can define a C# class or variable by using any name
or identifier that begins with an underscore or a letter,
that contains only letters or digits, and that is not a C#
reserved keyword


To create a C# program, you can use the Microsoft
Visual Studio environment or any text editor

39

Chapter Summary


After you write and save a program, you must compile
the source code


Program comments are nonexecuting statements that
add to document a program or to disable statements


As an alternative to using the command line, you can
compile and write your program within the Visual Studio
IDE


When you need to repeatedly use a class from the same
namespace, you can shorten the statements you type by
using a clause that indicates a namespace where the
class can be found