Basic C # Must Learn

C#

Program Structure Comments Data Types Constants Enumerations

Operators Choices Loops Arrays Functions

Strings Exception Handling Namespaces Classes / Interfaces Constructors / Destructors

Using Objects Struts Properties Console I/O File I/O

Program Structure C#
using System; namespace Hello {    public class HelloWorld {       public static void Main(string[] args) {          string name = "C#";          // See if an argument was passed from the command line          if (args.Length == 1)             name = args[0];          Console.WriteLine("Hello, " + name + "!");       }    } }
Comments C#
// Single line /* Multiple     line  */ /// <summary>XML comments on single line</summary> /** <summary>XML comments on multiple lines</summary> */
Data Types C#
Value Types bool byte, sbyte char short, ushort, int, uint, long, ulong float, double decimal DateTime   (not a built-in C# type) Reference Types object string Initializing bool correct = true; byte b = 0x2A;   // hex object person = null; string name = "Dwight"; char grade = 'B'; DateTime today = DateTime.Parse("12/31/2007 12:15:00"); decimal amount = 35.99m; float gpa = 2.9f; double pi = 3.14159265; long lTotal = 123456L; short sTotal = 123; ushort usTotal = 123; uint uiTotal = 123; ulong ulTotal = 123; Type Information int x; Console.WriteLine(x.GetType());              // Prints System.Int32 Console.WriteLine(typeof(int));               // Prints System.Int32 Console.WriteLine(x.GetType().Name);   // prints Int32 Type Conversion float d = 3.5f; int i = (int)d;   // set to 3  (truncates decimal)
Constants C#
	const int MAX_STUDENTS = 25; // Can set to a const or var; may be initialized in a constructor readonly float MIN_DIAMETER = 4.93f;
Enumerations C#
	enum Action {Start, Stop, Rewind, Forward}; enum Status {Flunk = 50, Pass = 70, Excel = 90}; Action a = Action.Stop; if (a != Action.Start)   Console.WriteLine(a + " is " + (int) a);    // Prints "Stop is 1" Console.WriteLine((int) Status.Pass);    // Prints 70 Console.WriteLine(Status.Pass);      // Prints Pass
Operators C#
	Comparison ==  <  >  <=  >=  != Arithmetic +  -  *  / %  (mod) /  (integer division if both operands are ints) Math.Pow(x, y) Assignment =  +=  -=  *=  /=   %=  &=  |=  ^=  <<=  >>=  ++  -- Bitwise &   |   ^   ~   <<   >> Logical &&   ||   &   |   ^   ! Note: && and || perform short-circuit logical evaluations String Concatenation +
Choices C#
	greeting = age < 20 ? "What's up?" : "Hello"; if (age < 20)   greeting = "What's up?"; else   greeting = "Hello"; // Multiple statements must be enclosed in {} if (x != 100 && y < 5) {     x *= 5;   y *= 2; } No need for _ or : since ; is used to terminate each statement. if (x > 5)   x *= y; else if (x == 5)   x += y; else if (x < 10)   x -= y; else   x /= y; // Every case must end with break or goto case switch (color) {                          // Must be integer or string   case "pink":   case "red":    r++;    break;   case "blue":   b++;   break;   case "green": g++;   break;   default:    other++;   break;       // break necessary on default }
Loops C#
	Pre-test Loops:   // no "until" keyword while (c < 10)   c++; for (c = 2; c <= 10; c += 2)   Console.WriteLine(c); Post-test Loop: do   c++; while (c < 10); // Array or collection looping string[] names = {"Fred", "Sue", "Barney"}; foreach (string s in names)   Console.WriteLine(s); // Breaking out of loops int i = 0; while (true) {   if (i == 5)     break;   i++; } // Continue to next iteration for (i = 0; i < 5; i++) {   if (i < 4)     continue;   Console.WriteLine(i);   // Only prints 4 }
Arrays C#
	int[] nums = {1, 2, 3}; for (int i = 0; i < nums.Length; i++)   Console.WriteLine(nums[i]); // 5 is the size of the array string[] names = new string[5]; names[0] = "David"; names[5] = "Bobby";   // Throws System.IndexOutOfRangeException // C# can't dynamically resize an array.  Just copy into new array. string[] names2 = new string[7]; Array.Copy(names, names2, names.Length);   // or names.CopyTo(names2, 0);  float[,] twoD = new float[rows, cols]; twoD[2,0] = 4.5f;  int[][] jagged = new int[3][] {   new int[5], new int[2], new int[3] }; jagged[0][4] = 5;
Functions C#
	// Pass by value (in, default), reference (in/out), and reference (out) void TestFunc(int x, ref int y, out int z) {   x++;    y++;   z = 5; } int a = 1, b = 1, c;  // c doesn't need initializing TestFunc(a, ref b, out c); Console.WriteLine("{0} {1} {2}", a, b, c);  // 1 2 5 // Accept variable number of arguments int Sum(params int[] nums) {   int sum = 0;   foreach (int i in nums)     sum += i;   return sum; } int total = Sum(4, 3, 2, 1);   // returns 10 /* C# doesn't support optional arguments/parameters.  Just create two different versions of the same function. */  void SayHello(string name, string prefix) {   Console.WriteLine("Greetings, " + prefix + " " + name); } void SayHello(string name) {   SayHello(name, ""); }
Strings C#
	Escape sequences \r    // carriage-return \n    // line-feed \t    // tab \\    // backslash \"    // quote // String concatenation string school = "Harding\t"; school = school + "University";   // school is "Harding (tab) University" // Chars char letter = school[0];            // letter is H letter = Convert.ToChar(65);     // letter is A letter = (char)65;                    // same thing char[] word = school.ToCharArray();   // word holds Harding // String literal string msg = @"File is c:\temp\x.dat"; // same as string msg = "File is c:\\temp\\x.dat"; // String comparison string mascot = "Bisons"; if (mascot == "Bisons")    // true if (mascot.Equals("Bisons"))   // true if (mascot.ToUpper().Equals("BISONS"))   // true if (mascot.CompareTo("Bisons") == 0)    // true Console.WriteLine(mascot.Substring(2, 3));    // Prints "son" // String matching // No Like equivalent - use regular expressions using System.Text.RegularExpressions; Regex r = new Regex(@"Jo[hH]. \d:*"); if (r.Match("John 3:16").Success)   // true // My birthday: Oct 12, 1973 DateTime dt = new DateTime(1973, 10, 12); string s = "My birthday: " + dt.ToString("MMM dd, yyyy"); // Mutable string System.Text.StringBuilder buffer = new System.Text.StringBuilder("two "); buffer.Append("three "); buffer.Insert(0, "one "); buffer.Replace("two", "TWO"); Console.WriteLine(buffer);     // Prints "one TWO three"
Exception Handling C#
	// Throw an exception Exception up = new Exception("Something is really wrong."); throw up;  // ha ha // Catch an exception try {   y = 0;   x = 10 / y; } catch (Exception ex) {   // Argument is optional, no "When" keyword   Console.WriteLine(ex.Message); } finally {   // Requires reference to the Microsoft.VisualBasic.dll   // assembly (pre .NET Framework v2.0)   Microsoft.VisualBasic.Interaction.Beep(); }
Namespaces C#
	namespace Harding.Compsci.Graphics {   ... } // or namespace Harding {   namespace Compsci {     namespace Graphics {       ...     }   } } using Harding.Compsci.Graphics;
Classes / Interfaces C#
	Accessibility keywords public private internal protected protected internal static // Inheritance class FootballGame : Competition {   ... } // Interface definition interface IAlarmClock {   ... } // Extending an interface  interface IAlarmClock : IClock {   ... } // Interface implementation class WristWatch : IAlarmClock, ITimer {    ... }
Constructors / Destructors C#
	class SuperHero {   private int _powerLevel;   public SuperHero() {      _powerLevel = 0;   }   public SuperHero(int powerLevel) {     this._powerLevel= powerLevel;   }   ~SuperHero() {     // Destructor code to free unmanaged resources.     // Implicitly creates a Finalize method   } }
Using Objects C#
	SuperHero hero = new SuperHero(); // No "With" construct hero.Name = "SpamMan"; hero.PowerLevel = 3; hero.Defend("Laura Jones"); SuperHero.Rest();   // Calling static method SuperHero hero2 = hero;   // Both reference the same object hero2.Name = "WormWoman"; Console.WriteLine(hero.Name);   // Prints WormWoman hero = null ;   // Free the object if (hero == null)   hero = new SuperHero(); Object obj = new SuperHero(); if (obj is SuperHero)   Console.WriteLine("Is a SuperHero object."); // Mark object for quick disposal using (StreamReader reader = File.OpenText("test.txt")) {   string line;   while ((line = reader.ReadLine()) != null)     Console.WriteLine(line); }
Structs C#
	struct StudentRecord {   public string name;   public float gpa;   public StudentRecord(string name, float gpa) {     this.name = name;     this.gpa = gpa;   } } StudentRecord stu = new StudentRecord("Bob", 3.5f); StudentRecord stu2 = stu;  stu2.name = "Sue"; Console.WriteLine(stu.name);    // Prints Bob Console.WriteLine(stu2.name);   // Prints Sue
Properties C#
	private int _size; public int Size {   get {     return _size;   }   set {     if (value < 0)       _size = 0;     else       _size = value;   } } foo.Size++;
Console I/O C#
	Console.Write("What's your name? "); string name = Console.ReadLine(); Console.Write("How old are you? "); int age = Convert.ToInt32(Console.ReadLine()); Console.WriteLine("{0} is {1} years old.", name, age); // or Console.WriteLine(name + " is " + age + " years old."); int c = Console.Read();  // Read single char Console.WriteLine(c);    // Prints 65 if user enters "A"
File I/O C#
	using System.IO; // Write out to text file StreamWriter writer = File.CreateText("c:\\myfile.txt"); writer.WriteLine("Out to file."); writer.Close(); // Read all lines from text file StreamReader reader = File.OpenText("c:\\myfile.txt"); string line = reader.ReadLine(); while (line != null) {   Console.WriteLine(line);   line = reader.ReadLine(); } reader.Close(); // Write out to binary file string str = "Text data"; int num = 123; BinaryWriter binWriter = new BinaryWriter(File.OpenWrite("c:\\myfile.dat")); binWriter.Write(str); binWriter.Write(num); binWriter.Close(); // Read from binary file BinaryReader binReader = new BinaryReader(File.OpenRead("c:\\myfile.dat")); str = binReader.ReadString(); num = binReader.ReadInt32(); binReader.Close();