Basics of C# programming

1. © Rays Technologies 1
C# BASICS
www.sunilos.com
www.raystec.com
10/14/16

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C#
Object Oriented Programming Language
Basic unit of C# is Object
An Object is an instances of Class
Class defines structure/skeleton of an
Object
The basic building blocks of C# is a Class
so a C# program is nothing but a class

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C#
Class contains methods and variables
Variables contains values
Methods perform operations
A Class should have default method
‘Main’ that is entry point of an
application

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Program
Procedural Language
int i = 5 //global variable
void main(){
..
a();
}
void a(int k){
int j = 0; //local variable
..
}

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Procedural Language Library
Library
Program 1 Program 2
Program 3 Program 4

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Class
C# Language
int i = 5 //global variable
void main(){
..
a();
}
void a(int k){
int j = 0; //local variable
..
}

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C # Library
Namespace
Class 1 Class 2
Class 3 Class 4

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C# Application
ApplicationApplication
Napspace 1 Namespace 2
Namespace 3 Namspace 4

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C# Program is a Class
public class HelloCSharp{
…….
}
A class may contain multiple variables and
methods
A Class should have default ‘Main’ method
that is an entry point for an application

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My First Program - HelloCSharp
 using System;
 public class HelloCSharp {
o public static void Main() {
o String name = “Vijay”;
o Console.WriteLine(“Hello” + name);
o }
 }
 using, public, class, static, and void are keywords
 Keywords are always written in small letters

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Compile & Run
Compile
o csc HelloCSharp.cs
o It will generate HelloCSharp.exe
Run
o HelloCSharp

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Keywords
class – is used to define a class
public – Access modifier shows accessibility of a
class or variable or method to other C# classes.
There are 3 access modifiers public, protected and
private
static – Memory for the static variables are
assigned only once in their life. Non-static
variables are called instance variables
void – is a NULL return type of Main method

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Commands
Console.write()/Console.WriteLine()
command is used to write text at standard
output device
String is a data type
Two strings are concated by + operator
o “Hello” + name

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Main method
 The Main method is sometimes called the application's
entry point.
 Can be declared as
 public static void Main(){}
 OR
 public static void Main(string args[]){}
 OR
public static int Main()
 {… return errorCode}
 OR
 public static int Main(string args[])
 {… return errorCode}

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While
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Print Hello C# 5 times - while
 using System;
 public class HelloWhile {
 public static void Main(String[] args) {
o boolean isAlive = true;
o int round = 0;
o while (isAlive) {
o Console.WriteLine(“Basanti will dance");
o round++;
o If(round>500 )
 isAlive =false;
o }
 }}

17. © Rays Technologies
For 10 Rs 5 shots
How
Much?
Okey!!
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For Loop
using System;
public class HelloFor {
public static void Main() {
ofor (int hits = 1; hits <= 5; hits++) {
Console.WriteLine( “Shot Balloon");
o}
o}
}
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Print Hello C# 5 times – do-while
using System;
public class HelloDoWhile {
public static void Main() {
o int i = 0;
o do {
 Console.WriteLine ( i+ “ Hello C#");
 i++;
o } while (i < 5);
}
}

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Add.java
using System;
public class Add {
public static void Main(String[] args) {
oint a = 5;
oint b = 10;
oint sum = a + b;
oConsole.WriteLine ("Sum is " + sum);
}
}

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switch
 public static void Main() {
 String country = “India”;
 switch(country) {
 case “India” :
o Console.WriteLine(“Language is Hindi");
o break;
 case “US” :
 case “England” :
o Console.WriteLine(“Language is English”);
o break;
 default :
o Console.WriteLine(“Don’t know language {0}”, country);
o break;
 }//switch
 }//method

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Value Types
int
long
sbyte
short
float
double
1
2
4
8
4
8
-128, +127
-9.223E18, +9.223E18
-32768, +32767
-2147483648, +2147483647
+3.4 E+38
+1.7 E+308
TypeType Size ByteSize Byte RangeRange
char 2 0, 65535 (Unicode)
bool 1 true, false
0
0
0
0
0
0
0
false
DefaultDefault

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Value Types
uint
ulong
byte
ushort
decimal
1
2
4
8
16
0, 255
0 .. 264-1
0, 65535
0,4294967295
± 1E-28 .. ±7.9E28
TypeType Size ByteSize Byte RangeRange
0
0
0
0
0
DefaultDefault

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Other Data Types
Reference types (composite)
o objects
o arrays
strings is a reference data type

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System.String class
 public static void Main() {
 String name = "Vijay Dinanth Chouhan";
 Console.WriteLine(" String Length- " + name.Length);
 Console.WriteLine(" 7 ths caharcter is- " + name[6]);
 Console.WriteLine(" Dina index is- " + name.IndexOf("Dina"));
 Console.WriteLine(" First i Position- " + name.IndexOf("i"));
 Console.WriteLine(" Last i Position- " + name.LastIndexOf("i"));
 Console.WriteLine(" a is replaced by b- " + name.Replace("a",
"b"));
 Console.WriteLine(" Chota vijay- " + name.ToLower());
 Console.WriteLine(" Bada vijay- " + name.ToUpper());
 Console.WriteLine(" Starts With Vijay- " +
name.StartsWith("Vijay"));
 Console.WriteLine(" Ends with han- " + name.EndsWith("han"));
 Console.WriteLine(" Substring- " + name.Substring(6));
 }

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System.Math class
 public static void main(String[] args) {
 Console.WriteLine("Math functions");
 Console.WriteLine(" Max 2,5 - " + Math.Max(2,5));
 Console.WriteLine(" Min 2,5 - " + Math.Min(2,5));
 Console.WriteLine(" Absolute 3.7 - " + Math.Abs(3.7));
 Console.WriteLine(" Exp 10 - " + Math.Exp(10));
 Console.WriteLine(" Square Root- " + Math.Sqrt(4));
 }

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Static vs Instance
String name = “Vijay”;
String surname = “Chohan”
C.WL(name.Length);
C.WL(surname.Length);
String.Length
C.WL(Math.Max(2,5));
C.WL(Math.Max(5,10));

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Hello <Name>
public class HelloName {
public static void Main(String[] args) {
 Console.WriteLine("Hello " + args[0]);
}
}

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Hello Name – if <condition>
 public class HelloName{
 public static void Main(String[] args) {
o if (args.Length == 1) {
 Console.WriteLine("Hello " + args[0]);
o } else {
 Console.WriteLine("Usage : HelloName <name>");
o }
 }
 }

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Hello All
public class HelloAll {
public static void Main(String[] args) {
o for (int i = 0; i < args.Length; i++) {
 Console.WriteLine(i + " = Hello " + args[i]);
o }
}
}

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Hello All - define Method
 public static void Main(String[] args) {
o PrintAll(args);
 }// main
 public static void PrintAll(String[] args) {
o int size = args.Length;
o for (int i = 0; i < size; i++) {
 Console.WriteLine((i + 1) + " = Hello " + args[i]);
o }
 }//myMethod

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Add.java
public class Add {
public static void Main(String[] args) {
o int a = Integer32.Parse(args[0]);
o int b = Integer32.Parse (args[1]);
o int sum = a + b;
o Console.WriteLine("Sum is " + sum);
}
}

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Division
public class Division {
public static void Main(String[] args) {
o int a = Integer32.Parse (args[0]);
o int b = Integer32.Parse (args[1]);
o double div = a/b;
o Console.WriteLine("Division is " + div);
}
}

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Return a Value
public class Division3 {
public static void Main(String[] args) {
o int a = Integer.Parse (args[0]);
o int b = Integer.Parse (args[1]);
o double div = getDivision(a, b);
o Console.WriteLine("Division is " + div);
}
 public static double getDivision(int a, int b) {
o double div = a / b;
o return div;
 }
 }

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10
One Dimension Array
20
[0]
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
Length
int[] table = new int[10];
int a = table[4];
int a = table[2];
int size = table.Length

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10
Initialize an Array
20
[0]
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
Length
int[] table = new int[10];
table[0] =2;
table[1] =4;
….
Or
int[] table =
{2,4,6,8,10,12,14,16,18,
20};

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Other Data Type Arrays
char[] chList = new char[5];
chList[0] = ‘A’….
Or
char[] chList = {‘A’,’B’,’C’,’D’,’E’}
String[] strList = new String[5];
strList[0] = “A”
strList[1] = “Bee”
Console.WriteLine(strList[0]);
….
Or
String[] strList = {“A”,”Bee”,”Cee”,”Dee”,”E”}

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2D Array
[0]
20
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
…
[0] [1] [2] [7] [8]
9
9
..
9
9
9
9
9

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 int[][] table = new int[10][9];
 table[1][5] = 5;
 int size = table.Length;
 int size = table[0].Length;
 int[][] rows = new int[10][];
 rows[0] = new int[9];
 rows[1] = new int[19];
 rows[2] = new int[29];
 int xyz = new int[10][9][2];

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Rectangular Array

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3D Array
20
[0]
18
..
10
8
6
4
2
[1]
[8]
[9]
[2]
[3]
[4]
[n]
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
[0] [1] [2] [8] [9]
20
18
..
10
8
6
4
2
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
20
18
..
10
8
6
4
30
27
..
15
12
9
6
20
18
..
10
8
6
4
2
30
27
..
15
12
9
6
3
40
36
..
20
16
12
8
4
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
90
81
..
45
36
27
18
9
100
90
..
50
40
30
20
10
…
[0]
[1]
[2]

42. Disclaimer
This is an educational presentation to enhance the
skill of computer science students.
This presentation is available for free to computer
science students.
Some internet images from different URLs are
used in this presentation to simplify technical
examples and correlate examples with the real
world.
We are grateful to owners of these URLs and
pictures.
© Rays Technologies 4210/14/16

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10/14/16