Lecture 2: C# Programming Basic syntax

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Lecture 2: C#

Programming Basic syntax

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Creating, Compiling, and Running

Your First C# Program

using System; class Example {

static void Main() {

Console.WriteLine("C# gives you programming power."); }

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Comments

C# supports three types of comments,

⚫ // single line comment

⚫ /* multiple line comments */

⚫ The third type of comment supported by C# is a

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Using System

⚫ Program is using the System namespace.

⚫ A namespace defines a declarative region.

⚫ A namespace provides a way to keep one set of names

separate from another.

⚫ Names declared in one namespace will not conflict with

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Static void Main

⚫ All C# applications begin execution by calling Main( ).

⚫ A method that is modified by static can be called before

an object of its class has been created.

⚫ This is necessary because Main( ) is called at program

startup.

⚫ The keyword void indicates that Main( ) does not return a

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WriteLine( )

⚫ WriteLine( ) displays the string that is passed to it.

⚫ Information that is passed to a method is called an argument.

⚫ In addition to strings, WriteLine( ) can be used to display other types of information, such as numeric data.

⚫ The Write( ) method is just like WriteLine( ), except that it does not output a new line after each call.

⚫ The line begins with Console, which is the name of a predefined class that supports console I/O.

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Algorithm For Calculating Area of a

Rectangle

:

⚫ Create a class “UseVars” or any name.(ﻢﺳا يأ)

⚫ Declare (ﻦﻠﻋأ) the variable – length , width.

⚫ Initialize (ﺔﺌﯿﮭﺗ) the variable – length,width.

⚫ Print the variable – length ,width.

⚫ Calculate (بﺎﺴﺣ) area of rectangle (ﻞﯿﻄﺘﺴﻤﻟا) .

⚫ Print the variable area.

LENGTH

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Variables

⚫ Variable is a named memory location that can be assigned a value. class UseVars {

static void Main() {

int length; // this declares a variable

int width; // this declares another variable int area; // this is a third variable

length = 9;

Console.WriteLine("length contains " + length);

width = 7;

Console.WriteLine("width contains " + width);

area = length * width;

Console.Write("area contains length * width: "); Console.WriteLine(area);

} }

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Output :

⚫ Length contains 9

⚫ Width contains 7

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The double Data Type

⚫ To allow numbers with fractional components, C#

defines two floating-point types: float and double, which represent single- and double-precision

values, respectively.

⚫ To declare a variable of type double, use a statement

similar to that shown here:

double result;

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Dynamic Initialization

⚫ C# allows variables to be initialized dynamically, using any expression valid at the point at which the variable is declared.

⚫ using System;

⚫ class DynInit {

⚫ static void Main() {

⚫ double radius = 4, height = 5;

⚫ // Dynamically initialize volume.

⚫ double volume = 3.1416 * radius * radius * height;

⚫ Console.WriteLine("Volume is " + volume);

⚫ }

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Operators

⚫ Arithmetic operators.

⚫ Relational Operators.

⚫ Bitwise Operators.

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Arithmetic Operators

Operator Operation

+ Addition

– Subtraction (also unary minus)

* Multiplication

/ Division

% Modulus

++ Increment

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% Operator

⚫ using System;

⚫ class ModDemo {

⚫ int iresult, irem;

⚫ double dresult, drem;

⚫ iresult = 10 / 3;

⚫ irem = 10 % 3;

⚫ dresult = 10.0 / 3.0;

⚫ drem = 10.0 % 3.0;

⚫ Console.WriteLine("Result and remainder of 10 / 3: " +

⚫ iresult + " " + irem);

⚫ Console.WriteLine("Result and remainder of 10.0 / 3.0: " +

⚫ dresult + " " + drem);

⚫ }

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⚫ 3 (quotient)

⚫ 3 | 10

⚫ 9

⚫ 1 (remainder)

⚫ The output from the program is shown here:

⚫ Result and remainder of 10 / 3: 3 1

⚫ Result and remainder of 10.0 / 3.0: 3.33333333333333 1

⚫ As you can see, the % yields a remainder of 1 for both

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Increment and Decrement

⚫ X = x + 1 is same as x++ ⚫ X= x – 1 is same as --X ⚫ x = 10; ⚫ y = ++x; ans : y =? ⚫ X = 10;

⚫ y = x++; ans : y=? and x = ?

⚫ x = 10; y = 2;

⚫ z = x++ - (x * y);

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Relational Operators

⚫ < Less than

⚫ <= Less than or equal to

⚫ > Greater than

⚫ >= Greater than or equal to

⚫ = = Equal to

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Bitwise Operator

⚫ & - AND

⚫ | - OR

⚫ ^ - XOR (exclusive OR)

⚫ || - Short-circuit OR

⚫ && - Short-circuit AND

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Table for Bitwise Operators

P Q P&Q P|Q p ^ q ~P

false false false false false true false true false true true true true false false true true false true true true true false false

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Assignment Operator

⚫ Variable op = expression

⚫ The operator pair += tells the compiler to assign to x the

value of x plus 10.

⚫ += –= *= /=

⚫ %= &= |= ^=

⚫ X += 10; is same as x=x+10;

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The if Statement

⚫ it is syntactically similar to the if statements in C, C++,

and Java. Its simplest form is shown

⚫ here:

⚫ if(condition) statement;

For Example

⚫ if(10 < 11) Console.WriteLine("10 is less than 11");

⚫ In this case, since 10 is less than 11, the conditional

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The for Loop

for(initialization; condition; iteration)

statement;

⚫ using System;

⚫ class ForDemo {

⚫ int count;

⚫ Console.WriteLine("Counting from 0 to 4:");

⚫ for(count = 0; count < 5; count = count+1)

⚫ Console.WriteLine(" count is " + count);

⚫ Console.WriteLine("Done!"); ⚫ } ⚫ } Output Counting from 0 to 4: count is 0 count is 1 count is 2 count is 3 count is 4 Done!

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While Loops

⚫ Condition is tested at the top of the Loop : If condition not satisfied then the loop will not be executed even once.

⚫ using System;

⚫ class WhileDemo {

⚫ char ch;

⚫ // Print the alphabet using a while loop.

⚫ ch = 'a'; ⚫ while(ch <= 'z') { ⚫ Console.Write(ch); ⚫ ch++; ⚫ } ⚫ } ⚫ }

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Do while Loops

⚫ Condition is tested at the bottom of the Loop –Do while will always execute atleast once.

⚫ using System;

⚫ class DWDemo {

⚫ char ch;

⚫ do {

⚫ Console.Write("Press a key followed by ENTER: ");

⚫ ch = (char) Console.Read(); // read a keypress

⚫ } while(ch != 'q');

⚫ }

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Usage of Break Statement

⚫ using System;

⚫ class Break2 {

⚫ char ch; ⚫ for( ; ; ) { ⚫ ch = (char) Console.Read(); ⚫ if(ch == 'q') break; ⚫ } ⚫ Console.WriteLine("You pressed q!"); ⚫ } ⚫ }

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Break – Comes out of Inner Loop

⚫ using System;

⚫ class Break3 {

⚫ for(int i=0; i<3; i++) {

⚫ Console.WriteLine("Outer loop count: " + i);

⚫ Console.Write(" Inner loop count: ");

⚫ int t = 0; ⚫ while(t < 100) { ⚫ if(t == 10) break; ⚫ Console.Write(t + " "); ⚫ t++; ⚫ } ⚫ Console.WriteLine(); ⚫ } ⚫ Console.WriteLine("Loops complete."); ⚫ } ⚫ }

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⚫ Outer loop count: 0

⚫ Inner loop count: 0 1 2 3 4 5 6 7 8 9

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Use continue

⚫ using System;

⚫ class ContDemo {

⚫ int i;

⚫ // Print even numbers between 0 and 100.

⚫ for(i = 0; i<=100; i++) {

⚫ // Iterate if i is odd. ⚫ if((i%2) != 0) continue; ⚫ Console.WriteLine(i); ⚫ } ⚫ } ⚫ }

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The C# Keywords

⚫ The reserved keywords cannot be used as names for variables, classes, or methods.

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Data Types

⚫ Integers

⚫ C# defines nine integer types:

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The Scope and Lifetime of

Variables

Difference between Scope and Lifetime?

⚫ Scope: It defines the visibility/accessibility of the variable

in a program.

⚫ Local variable - the scope is local to that function.

⚫ Static global variable - scope is limited to that file only.

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Lifetime of a Variable :

⚫ It is the duration of time for which the variable holds the

value during the execution of a program.

⚫ Local variable - the lifetime is within the functional block

in which it is declared. The memory allocated when function starts and deallocated when it terminates.

⚫ static variable - the life time will be the entire execution of

the program. value persists even between function calls.

⚫ Global variable - the life time will be the entire execution

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Operators

An operator is a symbol that tells the compiler

to perform a specific mathematical or logical manipulation. C# has four general classes of

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Logical Operators

Relational Operators

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Operator Precedence

R -> L

R -> L R-> L

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Inputting Characters from the

Keyboard

To read a character from the keyboard, call Console.Read( ). using System;

class KbIn {

static void Main() { char ch;

Console.Write("Press a key followed by ENTER: "); // Read a key from the keyboard.

ch = (char) Console.Read();

Console.WriteLine("Your key is: " + ch); }

}

output

Here is a sample run:

Press a key followed by ENTER: t Your key is: t

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To check if the character is same as

assigned character.

⚫ Create a class .

⚫ Declare the variable answer of type char .

⚫ Initialise the variable answer= ‘K’.

⚫ Print message “ Guess a letter between A and Z”

⚫ Read a character from user . Store it in ch.

⚫ If (answer = ch) then print “Right”

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The switch Statement

The general form of the switch statement is switch(expression) { case constant1: statement sequence break; case constant2: statement sequence break; case constant3: statement sequence break; . . . default: statement sequence break; }

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Example

using System;

class VowelsAndConsonants { static void Main() {

char ch; Console.Write("Enter a letter: "); ch = (char) Console.Read(); switch(ch) { case 'a': case 'e': case 'i': case 'o': case 'u': case 'y': Console.WriteLine("Letter is a vowel."); break; default: Console.WriteLine("Letter is a consonant."); break; } } }