Lecture 1
Introduction
Richard Gesick
Figures from Lewis, “C# Software Solutions”, Addison Wesley
Agenda
•
•
•
•
Overview of Programming Languages
Basics of C# and the IDE
Errors
Intro to Objects and Classes
1-2
Programming Languages
• A programming language specifies the words
and symbols that we can use to write a
program
• A programming language employs a set of
rules that dictate how the words and symbols
can be put together to form valid program
statements
1-3
Programming Languages
• Machine language
• Assembly language
• High-level languages
1-4
Machine & Assembly Languages
• Machine language
– Written in binary or hex
– Written using CPU instruction set
– Difficult to write, and not portable
• Assembly language
– Written using mnemonics for instructions and
symbolic names for variables
– Assembler converts code to machine language
– Easier to write, but still not portable
1-5
High-Level Languages
•
•
•
•
Examples: Fortran, Perl, COBOL, C++, Java
Highly symbolic
Portable among CPU architectures
Languages can be designed for specific uses:
– Perl: Internet applications
– Fortran: scientific applications
– COBOL: business applications
1-6
High-Level Languages
• Compiled
– Compiler converts source code (instructions and
data) into machine language, then program is
executed
• Interpreted
– Interpreter converts instructions into machine
language at run time as instructions are executed
– Usually executes more slowly than compiled
program
1-7
1-8
Programming Basics
• Programming is translating a problem into
ordered steps consisting of operations a
computer can perform:
– Input
– Calculations
– Comparisons of values
– Moving data
– Output
• The order of execution of instructions is
called flow of control
1-9
Four Types of Flow of Control
• Sequential Processing
– Execute instructions in order
• Method Call
– Jump to code in method, then return
• Selection
– Choose code to execute based on data value
• Looping or Iteration
– Repeat operations for multiple data values
1-10
Program Development
• The mechanics of developing a program include
several activities
– writing the program in a specific programming
language
– translating the program into a form that the computer
can execute
– investigating and fixing various types of errors that
can occur
• Software tools can be used to help with all parts
of this process
1-11
Problem Solving
• The purpose of writing a program is to solve a
problem
• Solving a problem consists of multiple
activities:
– Understand the problem
– Design a solution
– Consider alternatives and refine the solution
– Implement the solution
– Test the solution
• These activities are not purely linear – they
overlap and interact
1-12
Problem Solving
• The key to designing a solution is breaking it down
into manageable pieces
• When writing software, we design separate pieces
that are responsible for certain parts of the solution
• An object-oriented approach lends itself to this kind
of solution decomposition
• We will dissect our solutions into pieces called
objects and classes
1-13
Program Skeleton
1-14
1-15
Games Example
using System;
namespace CastleAttack
{
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
static void Main(string[] args)
{
using (CastleAttack game = new CastleAttack( ))
{
game.Run();
}
}
}
}
1-16
Identifiers
• Words in programs
• Categories:
– We make up
– Others make up
– Reserved in the language
1-17
C# Identifiers
• Letter followed by zero or more letters and
digits
• Case sensitive
1-18
1-19
1-20
White Space
• Spaces, blank lines, and tabs are called white space
• White space is used to separate words and symbols
in a program
• Extra white space is ignored
• A valid C# program can be formatted many ways
• Programs should be formatted to enhance
readability, using consistent indentation
1-21
Comments
• Comments in a program are called inline
documentation
• They should be included to explain the purpose of the
program and describe processing steps
• They do not affect how a program works
• C# comments can take two forms:
// this comment runs to the end of the line
/*
this comment runs to the terminating
symbol, even across line breaks
*/
1-22
Syntax and Semantics
• The syntax rules of a language define how we can put
together symbols, reserved words, and identifiers to
make a valid program
• The semantics of a program statement define what
that statement means (its purpose or role in a
program)
• A program that is syntactically correct is not
necessarily logically (semantically) correct
• A program will always do what we tell it to do, not
what we meant to tell it to do
1-23
Errors
• A program can have three types of errors
• The compiler will find syntax errors and other basic
problems (compile-time errors)
– If compile-time errors exist, an executable version of the
program is not created
• A problem can occur during program execution, such
as trying to divide by zero, which causes a program to
terminate abnormally (run-time errors)
• A program may run, but produce incorrect results,
perhaps using an incorrect formula (logical errors)
1-24
Program Errors
• Compiler errors
– Found by the compiler.
– Usually caused by incorrect syntax or spelling
• Run-time errors
– Reported by the system
– Usually caused by incorrect use of prewritten classes or
invalid data
• Logic errors
– Found by testing the program
– Incorrect program design or incorrect execution of the
design
1-25
Expect Errors
1-26
.NET
1-27
Program Structure
• In the C# programming language:
– A program is made up of one or more classes
– A class contains one or more methods
– A method contains program statements
• These terms will be explored in detail
throughout the course
• An application always contains a method
called Main
1-28
Object-oriented Programming (OOP)
• Class
– tool for encapsulating data and operations
(methods) into one package
– defines a template or model for creating and
manipulating objects
• Objects
– data created using the class and its methods
– an object is an instance of the class
– creating an object is instantiation
1-29
Objects
• An object has:
– state - descriptive characteristics
– behaviors - what it can do (or what can be done to it)
• The state of a bank account includes its current
balance
• The behaviors associated with a bank account
include the ability to make deposits and
withdrawals
• Note that the behavior of an object might change
its state
1-30
Classes
• An object is defined by a class
• A class is the blueprint of an object
• The class uses methods to define the behaviors of
the object
• The class that contains the main method of a C#
program represents the entire program
• A class represents a concept, and an object
represents the embodiment of that concept
• Multiple objects can be created from the same class
1-31
1-32
Objects and Classes
A class
(the concept)
An object
(the realization)
Bank
Account
John’s Bank Account
Balance: $5,257
Multiple objects
from the same class
Bill’s Bank Account
Balance: $1,245,069
Mary’s Bank Account
Balance: $16,833
Class and Object Example
• How would you
describe or define
these pictures?
• What are the
differences?
• What are the
similarities?
• Are you describing a
single entity or an
entire group of
entities?
1-34
What might the classes be? Objects?
Summary
• So what did you learn?
• Name three important concepts from the first
two lectures.
• What would I put on a test?