1. Lecture 1
Introduction
Richard Gesick

2. Agenda Overview of Programming Languages Basics of C# and the IDE
Errors
Intro to Objects and Classes

3. 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

4. Programming Languages
Machine language
Assembly language
High-level languages

5. 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
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6. High-Level Languages Examples: Fortran, Perl, COBOL, C++, Java, C#
Highly symbolic
Portable among CPU architectures
Languages can be designed for specific uses:
Perl: Internet applications
Fortran: scientific applications
COBOL: business applications

7. High-Level Languages Compiled Interpreted
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

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9. 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

10. 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

11. 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

12. 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

13. 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

15. Program Skeleton

16. Identifiers Words in programs Categories: We make up Others make up
Reserved in the language

17. C# Identifiers Letter followed by zero or more letters and digits
Case sensitive

18. C# Reserved Words

19. Unformatted Code Output:
This is a sample of a poorly formatted document.
It will run without problems
but is difficult to read and debug

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

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 */

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

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)

24. Program Errors Compiler errors Run-time errors Logic 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

25. Expect Errors

26. 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
An application always contains a method called Main

27. 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

28. 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

29. 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

30. Objects and Classes A class An object (the concept) (the realization)
Bank Account
A class
(the concept)
John’s Bank Account
Balance: $5,257
An object
(the realization)
Bill’s Bank Account
Balance: $1,245,069
Mary’s Bank Account
Balance: $16,833
Multiple objects
from the same class

31. 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?