Data Types are an integral part in any programming language. It represents how to express numbers, characters, strings, decimal point values etc. To illustrate, if you want to express 25 in C#, you can write a code as shown below:

int x = 25
In the above code, int represents the integer data type. x denotes a variable name. Variables are nothing but a storage area in the memory. 25 is the value for the variable x. Without a variable you cannot store values. Keep in mind that int is an alias for the data type Integer. It is having a fixed limit beyond which the data type will not hold values. 
Like Integer, all data types are having aliases and a fixed range of values. You should use a data type best suited to your programming needs. For example, if you are writing code for developing a calculator, it’s better to use data types, which will accept large values. This will avoid runtime program errors. 
Let’s look at another scenario. The data type Byte accepts values only up to 255. If you try to apply a value of 300 for the corresponding variable, there will be errors during the execution of the program. These errors are called as Exceptions, which will be discussed in an another article. If you had applied the data type Integer for the above program, this problem would have been avoided. Please go through Table 1 for a detailed list of all data types. 
Table 1
System.Byte –> byte 
System.Sbyte –> sbyte 
System.Int16 –> short 
System.Int32 –> int 
System.Int64 –> long 
System.UInt16 –> ushort 
System.UInt32 –> uint 
System.UInt64 –> ulong 
System.Single –> float 
System.Double –> double 
System.Object –> object 
System.Char –> char 
System.String –> string 
System.Decimal –> decimal 
System.Boolean –> boolean 
Basically, data types in C# are classified into two, viz; Value based and reference based types. Let’s examine each of these types in detail. Value Based Data Types include all numerical data types like Integer, Float, Byte and etc. Here you are working directly with values. When you try to assign one value type to another, a bit wise copy is achieved as shown in the listing given below:
using System; 
struct Valdata  
{ 
public int a; 
public int b; 
} 
class Valtype  
{ 
public static void Main(string[] args)  
{   
Valdata v = new Valdata(); 
v.a = 200; 
v.b = 300; 
Valdata v1 = v; 
Console.WriteLine(v.a); 
Console.WriteLine(v.b); 
Console.WriteLine(v1.a); 
Console.WriteLine(v1.b);   
Console.WriteLine("##################################"); 
v1.a = 800; 
Console.WriteLine(v1.a); 
Console.WriteLine(v.a); 
} 
} 
Note that even if you change the values of one variable, the value of another variable won’t change. Reference types include Classes and Interfaces. Here, if you change the value of one variable the value of the other variable also reflects the same value. Also, after creating an object of a class, you are working directly on that object and not with the actual values as in value types. Hence copies of reference types results in a shallow copy. To illustrate, change the definition of the above type from a C# structure to a C# class (in the above code) and observe the result.
Boxing and Unboxing 
The conversion of a value type into a reference type is termed as boxing while the conversion of a reference type into value type is termed as unboxing. Verify the code given below: 
// Value type
int x = 100; 
// x boxed to a object type which is reference based, no explicit cast required 
object Y = X;    
// y unboxed to an integer type, explicit cast required while unboxing
int Z = (int)Y 
 
Programming Constructs
In this session, we will discuss about the commonly used programming constructs like if-else, Switch-case, for, while, do-while loops. Let’s analyze each one of them in detail
If – else
This is one of the popular decision making statements, which is similar to that of its C+= and Java counterparts. Its usage is given below
Usage 
if(Condition) 
{ 
Statements 
} 
else  
{ 
Statements 
} 

If the condition satisfies, the statements inside the if block will be executed, otherwise statements inside the else part will execute as shown in Listing 4:
Listing 4 
using System; 
class Fund 
{ 
public static void Main() 
{ 
int x1 = 50; 
int x2 = 100; 
if(x1>x2) 
{ 
Console.WriteLine(“X1 is greater”); 
else 
Console.WriteLine(“X2 is greater”)  
} 
} 
} 
Switch – Case
This is also one of the decision making statement which is regarded as an alternative to if – else. Its usage is given below
Usage
switch(expression)  
{ 
case 10: Number is 10;break 
case 20: Number is 20;break 
case else: Illegal Entry;break 
} 
When the expression matches with a case value, the corresponding statements would be printed. Listing 5 explains the usage of Switch – Case statement.
Listing 5 

    
using System; 
class Switchexample { 

public static void Main() { 

int wday = 2; 

switch(wday) { 

case 1: Console.WriteLine(“Monday”);

break; 

case 2: Console.WriteLine(“Tuesday”);

break; 

} 

} 

} 
Looping Statements 
For loop 
This loop is used to iterate a value fixed number of times. Its usage is given below:
Usage 
for(Initial Value, Condition, Incrementation / Decrementation) 

{ 

  Statements

} 
You have to specify Incrementation and Decrementation using ++ and – operators. Listing 6 examines the working of for loop. Here, numbers from 1 to 10 will be printed as output. 10 will also be printed because we have used <= operator. Try using only < operator and observe the result.
Listing 6
using System; 

class Forexample { 

public static void Main() { 

for(int I = 1; I<=10;I++) { 

Console.WriteLine(I); 

} 

} 
While loop
This loop is similar to for loop, except that condition is specified first and is used to repeat a statement as long as a particular condition is true. The usage of while loop is given below:
while(Condition) 

{ 

Statements

} 

If the condition is false, statements within the loop will not be executed. Listing 7 examines the working of while loop:
Listing 7
using System; 

class Whileexample 

{ 

public static void Main() 

{ 

int I = 1; 

while(I <=10) 

{ 

console.WriteLine(I); 

}

}
Do- While
This looping statement is also similar to that of the previous one but the condition is specified last. Its usage is given below:
Usage 
do 
{ 
Statements 
}while(Condition)
In this case, the condition is tested at the end of the loop. Hence the statements within the loop are executed at least once even if the condition is false. Let’s verify an example:
Listing 8
using System; 


class Whileexample 


{ 


public static void Main() 


{ 


do 


{ 


int I = 1; 


} 


while(I<=10); 


Console.WriteLine(I); 


} 


} 




Foreach 


If you had used Visual Basic then you would be familiar with foreach statement. C# also supports this statement. Listing 9 illustrates the usage of this statement:
Listing 9 
using System; 


using System.Collections; 


class Foreachdemo { 


public ArrayList numbers; 


Foreachdemo() { 


numbers = new ArrayList(); 


numbers.Add("One"); 


numbers.Add("Two"); 


numbers.Add("Three"); 


numbers.Add("Four"); 


numbers.Add("Five"); 


} 


public static void Main() { 


Foreachdemo fed = new Foreachdemo(); 


foreach(string num in fed.numbers) { 


Console.WriteLine("{0}",num); 


} 


} 


} 


In the above example, an object of type ArrayList is created and values are added to it using the Add method of the ArrayList class. Try removing the second using directive and observe the result
Break Statement 
This statement is used to terminate a loop abruptly. We have seen the usage of this statement while discussing decision-making statements. Listing 10 examines the working of this statement.
Listing 10 
using System; 


class Whileexample 


{ 


public static void Main() 


{ 


for(int I = 1; I<=10; I++) 


{ 


Console.WriteLine(I); 


if(I==5) 


{ 


break; 


} 


} 


} 

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