Revision as of 23:44, 10 January 2006

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/library/default.asp?url=/library/en-us/dncenet/html/tchCJavaComparingProgrammingLanguages.asp

Basic Data Types

C# is a strongly typed language. This means every object in C# must be declared to be of a specific type. Variable Types

Variables must be declared with an identifier and then initialized.

Declaration

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.

// declare a variable int firstInt; string myString;

Initialization

Initialization actually sets the variables value

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

other ways to do it

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

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

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

   int UsedBeforeInit;
   Console.WriteLine(UsedBeforeInit);

will produce

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

       'UsedBeforeInit'

UsedBeforeInit.aspx - web example of misused variable source UsedBeforeInit_Fixed.aspx - 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

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

Use on method names method names.

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

use for variable names Other Coding Techniques and practices Microsoft - Coding Techniques and Programming Practices IBM Best Practices for Programming in C GNU Coding Standards GNU Naming conventions More Types

Operators

ECMA-334 Operators and punctuators

C# uses the equals = sign for Assignment

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

Mathematical Operators

Increment Decrement Operators

Operator Precedence

Evaluated First

   * ++,--,unary-
   * *,/,%
   * +,-

Evaluated Last

   * =,+=,-=,*=,etc

+ is also used to concatenate strings

<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 + ".");</csharp>
    

will output (remember \n is a new line)

    Super string theory!!!!
    Is really cool.

Short in class Assignment In class assignment 10-15 mins Build a c# console app (remember to take a takedown aproach start small with somethin you know)

   * 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

Once the console application is done convert it to work on a web page using Response.Write instead of Console.WriteLine

Top down development with comments /infod/jeff/classsource/class2/topdown.aspx Fully implemeted Console adding program /infod/jeff/classsource/class2/add.cs Conversions and Casting

Casting is the process of converting form one type of object to another, There are two Conversion types in C# implicit and explicit. Implicit conversion is handled by the compiler and requires no extra work. Implicit conversion is only possible if the new data type can hold the old data type with out any data loss. explicit conversion forces on datatype into another even if it doesn't fit. It is up to the programmer to define explicit casts. implicit conversion

<csharp>int intNumber = 1000; long lngNumber; lngNumber = intNumber;

int Number1= 6; int Number2= 5; int Number3 = Number1 / Number2; //Number3 == 1 </csharp>

explicit conversion

<csharp>long lngNumber = 1000; int intNumber; intNumber = (int)lngNumber;

int Number1= 6; int Number2= 5; double Number3 = (double)Number1 / (double)Number2; //Number3 == 1.2</csharp>

Constants

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>

example

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

Arrays

Arrays are groups of variables of the same type Syntax

<csharp>type [] identifier</csharp>

single dimension arrays

 		<csharp>string [] aryNames = new string[3];
 		
 		aryNames [0] = "Joe";
 		aryNames [1] = "Mike";
 		aryNames [2] = "Alice";</csharp>

Example single dimensions array singleArrray.aspx Source multi dimension arrays

		<csharp>string [,] aryNames = new string[3,3];

aryNames [0,0] = "Joe"; aryNames [0,1] = "Schmoe"; aryNames [0,2] = "111 111-1111"; aryNames [1,0] = "Mike"; aryNames [1,1] = "Orbinawitz"; aryNames [1,2] = "222 222-2222"; aryNames [2,0] = "Mary"; aryNames [2,1] = "Alice"; aryNames [2,2] = "333 333-3333";</csharp>

Example multi dimensions array multiArrray.aspx Source jagged arrays

<csharp>string [][] aryNames = new string[3][];

aryNames[0] = new string[2]; aryNames[1] = new string[4]; aryNames[2] = new string[3];

aryNames [0][0] = "John"; aryNames [0][1] = "Doe";

aryNames [1][0] = "James"; aryNames [1][1] = "Bond"; aryNames [1][2] = "007"; aryNames [1][3] = "License to kill";

aryNames [2][0] = "Mary"; aryNames [2][1] = "Alice"; aryNames [2][2] = "Im not a number im a free woman";</csharp>

Example jagged array jaggedArrray.aspx Source even more array samples

<csharp>using System;

class Array { public static void Main() { //array of ints int[] myInts = {5,10,15}; Console.WriteLine("array of ints:"); Console.WriteLine( "myInts[0]: {0}, myInts[1]: {1}, myInts[2]:{2}" ,myInts[0],myInts[1],myInts[2]);

//jagged array of bools bool[][] myBools = new bool[2][]; myBools[0] = new bool[2]; myBools[1] = new bool[1];

myBools[0][0] = true; myBools[0][1] = false; myBools[1][0] = true; Console.WriteLine("jagged array of bools:"); Console.WriteLine( "myBools[0][0]: {0}, myBools[1][0]: {1}", myBools[0][0], myBools[1][0]);

//multi-dimensional array of doubles double[,] myDoubles = new double[2,2]; myDoubles[0, 0] = 3.147; myDoubles[0, 1] = 7.157; myDoubles[1, 1] = 2.117; myDoubles[1, 0] = 56.00138917; Console.WriteLine("multi-dimensional array of doubles:"); Console.WriteLine("myDoubles[0, 0]: {0}, myDoubles[1, 0]: {1}", myDoubles[0, 0], myDoubles[1, 0]);

//array of strings string[] myStrings = new string[3]; myStrings[0] = "Joe"; myStrings[1] = "Matt"; myStrings[2] = "Robert"; Console.WriteLine("array of strings:"); Console.WriteLine("myStrings[0]: {0}, myStrings[1]: {1}, myStrings[2]: {2}", myStrings[0], myStrings[1], myStrings[2]); } }</csharp>

==Structs

Lightweight alternatives to classes. Structs do not support inheritance or destructors. Don't worry if you don't understand structs yet it hard cuz the book teaches them before classes. We will talk more about stucts after we talk about classes Syntax

[ attributes] [access-modifiers] struct identifier [:interface-list {struct members}

struct Dog {

public string name;
public string weight;
public int age;

}

Enumerators

Enumerators are used to set predefined list of named constants. Syntax

[ attributes] [modifiers] enum identifier [:base-type {enumerator-list};

 //An enumerator for ServingSizes at BK
 enum ServingSizes : uint
 {
   Small = 0,
   Regular = 1,
   Large = 2,
   SuperSize = 3
 }
 
 //another more usefull example
 // forced sequence to start  
 // from 1 instead of 0 (default)
 enum Months 
 {
   January = 1, February , March, April ,
   May , June , July , August , Sept , Oct , Nov , Dec 
 }

HomeWork

• Learning c#
• Chapter 6, Chapter 7 47-84

• Build a console application

  Variable Types and Casting 4pts 1 extra credit
  Build a console application that declares and initializes three integers with watever values you like
  Display these integers in the console
  Cast the intergers into three floats
  Display the floats
  Cast the integers into three strings
  Display the strings
  Put the strings into an array
  Display the array

  extra credit use an enumerator to change word stings into ints ie "one" = 1 "two" = 2

codetoad.com ASP.NET : HTML Server Controls aspalliance.com - ASP.NET Syntax for Web Server Controls Next week Quiz on weeks 1 and 2

Links

A Comparative Overview of C# Introduction to ASP .NET and Web Forms - uses VB.Net Microsoft - Coding Techniques and Programming Practices IBM Best Practices for Programming in C GNU Coding Standards GNU Naming conventions RFC 2068 HTTP/1.1 Review