2: Variables, Datatypes and Their Usage in C#

What is Variable?

A variable is entity whose value can keep changing.

For example, the age of a person, and increment or salary of an employee

In c#, the memory is allocated at the time of variable creation.

Syntax:

<data type><variable name> // declaring variable

<variable name>// initialization

Let’s talk about the name and age of a student.

As you learn before in C languages Name should be string, and age should be integer

So,

String studentName;

studentName=”Muhammad Wasim”;

int studentAge;

studentAge=23;

Observe that the first letter of an identifier is lowercase and the first letter of each subsequent concatenated word is capitalized. E.g. studentName, studentAge this is called camel notation. Microsoft recommends camel notation for C# variables, do not use reserved keywords, see reserved keywords

http://msdn.microsoft.com/en-us/library/x53a06bb.aspx

Data types:

When you go to shop for buying milk and flour etc. the shopkeeper always give you milk in water proof bag but do not give you in normal paper bag like he gives flour. Similarly the compiler does not know which type of data you want to give it. It may be string type or integer type or character etc.

When you declare a variable the data type is assign to the variable like in below example.

String studentName;

In C# data types are divided into two types,

 1) Value type

 2) Reference type

Value type

Variable of value types are stored in stack. These variables store actual values, these values can either be user define or predefined data type.

Most of the built-in data types are value type like int, float, double, char bool etc.

Reference type

Variable of reference type store the memory address of other variable in a heap, these values can either be user define or predefined data type.

Like string is built-in data type but it is reference type, but most of the user define data types are reference type like class, interface, array, and delegate.

We will talk about all the reference type later in our coming posts.

Let’s talk about student class. We will see class later in depth.

Here you can see student class is stored in heap(heap located in  RAM) which is reference type and its variable(studentAge) is value type.

Predefined Data type

Literals in C#

A literal is a static value assign to the variables. We can define literals for any data type in C sharp.

Types:            

1. Boolean Literal
2. Integer Literal
3. Real Literal
4. Character Literal
5. String Literal
6. Null Literal

Boolean Literal:

Boolean literal have two values, false, true

Bool myBoolValue=false;

Where false is a boolean literal assign to the boolean literal.

Interger Literal:

Integer Literal can be assign to int, long etc data types.

Suffixes are U, L, UL or LU where U is use for uint or ulong, L is use for long and LU or UL is use for ulong.

long myLongValue=1000L;

Where 1000L is a integer literal assign to the myLongValue variable.

Real Literal

A real literal can be use for float, decimal  and double.

Suffixes are F, D and M where F is use for float, D is use for Double and M is use for Decimal.

Float myFloatValue=4.54F;

Where 4.54F is a real Literal assign to the myFloatValue variable.

Character Literal

Character Literal can be use for character data type.

It is simple define as

char myCharValue=’w’

where w is a character literal assign to the myCharValue variable.

String Literal

There are two types of string Literals

1.   Regular string literal
2.   Verbatim string literal

Regular can be define as

string myStringValue=”Dot Net”;

Verbatim is similar to the regular string Literal but it start with @ symbol.

string myStringValue=”@hotmail.com”;

Null Literal

Null literal is only one value which is “Null”

string myNullValue=null;

Character Escape Sequence in C#

Character Escape sequence is use for formatting the string data.

Here are some examples using Character Escape Sequence you can use above escape sequence for learning .

Console.WriteLine("Muhammad\nwasim"); //new line operator

Console.WriteLine("Welcome \'Friends\'");// single quote

Console.WriteLine("laptop\t PC");// tab sequence

Merging and Concatenation

Merging are concatenation are two ways for formatting text when using Console.WriteLine() method.

PlaceHolder

PlaceHolder is use for concatenate the text before display the output,

It use braces with zero based index to indicate the position of suitable value

For example:

int num1=10;

int num2=5;        

Console.WriteLine("Number one is {0} and Number two is {1}",num1, num2);

Merging can also perform the above operation without using index for position of the suitable variable.

Below example works similar to the above example

Console.WriteLine("Number one is " + num1 + " and Number two is " + num2);

Taking Value From User

In C language you simply define in Scanf() function the type of data that should be taken by the user but in c sharp there is no such a function but there is a method called Console.Readline() which always take string value from the user.

Example:

string name;

Console.WriteLine("Please Enter Your Name");

name = Console.ReadLine();

Console.WriteLine("your Name is {0}",name);

Console.ReadLine();

Notice that we have taken value in string name variable at this point the cursor waits for input see below 

What Happen when you get inter value from Console.ReadLine() method.

Yes it show compile time exception which is “Cannot implicity convert type string to int”, as I define above that Console.ReadLine() only take string value from the user not like scanf() in C.

This issue can be remove by the convert class for converting string to integer.

Convert class provide you many method like ToDouble, ToChar, ToDecimal etc you can explore more pressing ‘.’ After writing Convert

Soon We Will See Type Casting and its Types.

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