Difference between revisions of "OOP Class2"

esse quam videri
Jump to: navigation, search
Line 393: Line 393:
Create a web page that does the same thing.

Revision as of 18:09, 27 May 2009


Posting home work and website

C# fundamentals

Questions from week 1 reading. discussion

Some pages comparing c# to other languages

A Comparative Overview of C# http://genamics.com/developer/csharp_comparative.htm

C# and Java: Comparing Programming Languages http://msdn.microsoft.com/en-us/library/ms836794.aspx



Common Language Runtime


organizing classes with hierarchy


reserved system word


Microsoft Intermediary Language


Just In Time compilation @ first run

Everything is an Object

In c# everything is an object. And all objects inherit from the object class.

See object in the classbrowser

Since all objects inherit from the object class they all have some the basic functionality like a method called ToString();

See the source for object.cs from mono

Basic Data Types

C# is a strongly typed language. This means every object in C# must be declared to be of a specific type. All of c# basic varible type inherit from System.Object

Variable Types

.NET Types
Type Size in Bytes .Net Type Description
byte 1 Byte Unsigned (0-255)
char 2 Char Unicode Characters ascii unicode and other
bool 1 Boolean True of False
(Note: C# boolean values do not equate to integer values, or True != (read as is not equal to) 1 and False != 0)
sbyte 1 SByte Signed integers(-128 to 127)
short 2 Int16 Signed integers(-32,768 to 32,767)
ushort 2 UInt16 Unsigned integers(0 to 65,535)
int 4 Int32 Signed integers(-2,147,483,648 to 2,147,483,647)
uint 4 UInt32 Unsigned integers(0 to 4,294,967,295)
float 4 Single fixed-precision up to 7 digits. Floating point number ( 1.5 x 10-45 to 3.4 x 1038 )
double 8 Double fixed-precision up to 16 digits. Floating point number ( 5.0 x 10-324 to 1.7 x 10308 )
decimal 12 Decimal fixed-precision up to 28 digits. Typically used for financial calculations. Required the suffix "m" or "M"
long 8 Int64 Signed integer ( -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807)
ulong 8 UInt64 Unsigned integer (0 to 18,446,744,073,709,551,615 )

Variables must be declared with an identifier and then initialized.


Declaration sets aside a named section of memory the is the proper size to hold the declared type. At this point the variable contains nothing.

<csharp>// declare a variable int firstInt; //declares a vaiable of type int string myString; //declares a vaiable of type string</csharp>


Initialization actually sets the variables value

<csharp>// initialize the variable firstInt = 1; myString = "Hello!";</csharp>

Initialization uses the assignment operator to set the value of a variable


The Assignment operator in c# is the '=' sign. You can assign variables like this...


The Assignment operator in c# is the '=' sign. You can assign variables like this...

We'll learn more about operators later.

other ways to do it

<csharp>// declare some variables int secondInt, thirdInt, fourthInt; secondInt = 2; thirdInt = 3; fourthInt = 4;

//declare and initialize variables in one line int myNegativeInt = -2147483648;</csharp>

In c# variables cannot be used unil they are initalized. For example

<csharp>int UsedBeforeInit; Console.WriteLine(UsedBeforeInit);</csharp>

will produce

  helloError4.cs(10,31): error CS0165: Use of unassigned local variable 'UsedBeforeInit'

Compiler Errors

  helloError4.cs(10,31): error CS0165: Use of unassigned local variable 'UsedBeforeInit'
  file            Line        .Net Framework error # and description

Csharp warning CS0168: The variable 'NeverUsed' is declared but never used

UsedBeforeInit.cs - example of misused variable
UsedBeforeInit_Fixed.cs - all beter now source

More examples of built in types 1x1.cs C# intrinsic types from Learn-C-Sharp. variable.aspx - example from book aspx page View Source variable2.aspx = example from book errors View Source

Variable Names

Variable should be named with meaningful names.

for exmaple

z = x * y;

does not convey any meaning


distance = speed * time;

does convey meaning. If varibales are named properly it can make your code mush easier to read.

Naming conventions

Name variables intelligently.
Name variables with names that have meaning.

Hungarian Notation

Hungarian notation id a popular notation system used be many C, C++ and VB programmers. It was originally devised in Charles Simonyi's doctoral thesis, "Meta-Programming: A Software Production Method." Hungarian notation specifies that a prefix be added to each variable that indicated that variables type. It also specifies sometimes adding a suffice to clarify variables meaning. In the early 1980's Microsoft adopted this notation system.

ie... intHitCounter, intHitsPerMonthMax

Hungarian Notation - Charles Simonyi Microsoft


PascalNotation Capitalize first Letter and then the first letter on each word.
ie... PascalNotation, IntVarName

Use on method names method names.

camelNotation Lower case first letter and then capitalize the first letter of each word
ie... camelNotation, intVarName

use for variable names

Other Coding Techniques and practices
[http://msdn.microsoft.com/en-us/library/ms229002.aspx .NET Framework Developer's Guide Guidelines for Names]
IBM Best Practices for Programming in C
GNU Coding Standards
GNU Naming conventions
More Types


ECMA-334 Operators and punctuators

C# uses the equals = sign for Assignment

int myVar = 15;			 //sets the value of myVar to 15

Mathematical Operators

Operator Description
* multiplication
/ division
% modulus remainder Ask Dr.Math What is Modulus?

Increment Decrement Operators

Operator Description
+ increment same as foo = foo + 1
-- decrement same as foo = foo - 1
= calculate and reassign addition
-= calculate and reassign subtraction
*= calculate and reassign multiplication
/= calculate and reassign division
%= calculate and reassign modulus
y= x++ assignment prefix y is assigned to x and then x in incremented
y= ++x assignment postfix x is incremented and then assigned to y

Operator Precedence

Evaluated First

  • ++,--,unary-
  • *,/,%
  • +,-

Evaluated Last

  • =,+=,-=,*=,etc


Strings are an object in c#

String concatenation

+ is also used to concatenate strings

If you have two string that you want to combine into one string you can concatenate them. Or use the super jedi .net method String.Format method

<csharp>//Create a string and set it's value to "cool." string coolString = "cool"; //Do some concatenations and make it super cool Console.WriteLine ("Super " + "string " + "theory!!!\n" + "Is really " + coolString + ".");

string notherCoolString = "another " + coolString + " string."; Console.WriteLine(notherCoolString);

Console.WriteLine(String.Format("In Line formating of '{0}'", notherCoolString));


will output (remember \n is a new line)

    Super string theory!!!!
    Is really cool.
    another cool string.
    In Line formating of 'another cool string.'

Escape Sequences

The backslash character is used as a string escape sequence. It will escape the next character and change it's meaning. For example \" with output a ", \n with out put a newline and \\ with output a single \.

  Short in class Assignment
  In class assignment 10-15 mins
  Build a c# console app (remember to take a top down aproach start small with something you know maybe start with hello world)
   * Declare and initialize two integers
   * Display their values using Console.WriteLine
   * Declare a third integer and initialize it with the sum of the first two integers
   * Output the value of the third integer

Top down development with comments topdown.aspx

Fully implemented Console adding program add.cs

<csharp> using System; using System.Collections.Generic; using System.Text;

namespace Hello {

   class Program
       static void Main(string[] args)
           Console.WriteLine("Super Cool Calculatorizer");
           //Declare two variables
           int intOne;
           int intTwo;
           int intSum;
           //intialize the two variables
           intOne = 47;
           intTwo = 2;
           //Lets test the values
           Console.Write("Enter a integer: ");
           intOne = int.Parse(Console.ReadLine());     //set the value of intOne 
                                                       //to what was typed in the console
           Console.Write("Enter another integer: ");
           intTwo = int.Parse(Console.ReadLine());     //int.Parse attempts to parse a string
                                                       //and convert it to an int
           intSum = intOne + intTwo;
           Console.WriteLine("intTwo + intTwo =  " + intSum);

} </csharp>


Constants are datatypes that will be assigned a value that will be constant thought the executing of the code. You cannot change constants once they have been assigned a value. syntax

<csharp>const type identifier = value;</csharp>


<csharp>const int freezingPoint = 32; const int freezingPointMetric = 0; const float pi = 3.141592</csharp>

OOP Arrays

Simple Branching



<csharp>if (expression)

   // statement

if (expression) {

   // statements
   // statements

} if (expression) {

   // statements
   // statements

} else {

   // statements



  • Learning c#
  • Chapter 5, Chapter 6

Create a simple text game that asks three questions and set three variables. The program should run in the console and use.

  • Console.WriteLine
  • Console.ReadLine
  • Ints, Strings and ifs

Analysis of Homework Project

  • On very structured programs like the one analysis is quite easy
    • Start by indentifing the steps
    • Add Pseudocode as c# comments for each step
    • Fill in the real syntax for each step and compile each time to make sure nothing breaks (I like to call this baby steps and I like to use this technique whenever I'm trying to implement something that is completely new to me)

The pseudocode might look something like <csharp>using System; namespace HelloVariables {

   class VariablesAndCasting
       public static void Main()
           Console.WriteLine("3 Questions");
           //A simple game that asks three questions and checks the answers. If the question is answered correctly we will award 1 point
           //Declare Variables
           //Ask Question 1
           //Read Answer
           //Check Answer and add 1 to points is correct
           //Reapeat with Questions 2 and 3
           //Display Percent Correct



Create a web page that does the same thing.