Use of Checked and Unchecked keyword in C#

Here I am going to explain what the use of checked and unchecked keyword in C#. Here I am taking the some content from MSDN to explain about it. A checked context, arithmetic overflow raises an exception. In an unchecked context, arithmetic overflow is ignored and the result is truncated.

• Checked Specify checked context.
• unchecked Specify unchecked context.

The following operations are affected by the overflow checking:

• Expressions using the following predefined operators on integral types:
  ++ — - (unary) + - * /
• Explicit numeric conversions between integral types.

The checked/unchecked compiler option lets you specify checked or unchecked context for all integer arithmetic statements that are not explicitly in the scope of a checked or unchecked keyword. Now I am going to explain one by one.

Checked

The checked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions. It can be used as an operator or a statement according to the following forms.

The checked statement:

checked block

The statement block that contains the expressions to be evaluated in a checked context.

The checked operator:

checked (expression)

The expression to be evaluated in a checked context. Notice that the expression must be in parentheses ( ).

Unchecked

The unchecked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions. It can be used as an operator or a statement according to the following forms.

The unchecked statement :

unchecked block

The statement block that contains the expressions to be evaluated in an unchecked context.

The unchecked operator :

unchecked (expression)

The expression to be evaluated in an unchecked context. Notice that the expression must be in parentheses ( ).

Example

namespace Checked_Unchecked

{

class Program

{

public short a = 30000;

public short b = 20000;

public short c;

public int Add()

{

try

{

c = checked((short)(a + b));

}

catch (System.OverflowException e)

{

System.Console.WriteLine(e.ToString());

}

return c;

}

public int Mul()

{

try

{

checked

{

c = (short)(a * b);

}

}

catch (System.OverflowException e)

{

System.Console.WriteLine(e.ToString());

}

return c;

}

public int Add_Unchecked()

{

try

{

c = unchecked((short)(a + b));

}

catch (System.OverflowException e)

{

System.Console.WriteLine(e.ToString());

}

return c;

}

public int Mul_Unchecked()

{

try

{

unchecked

{

c = (short)(a * b);

}

}

catch (System.OverflowException e)

{

System.Console.WriteLine(e.ToString());

}

return c;

}

static void Main(string[] args)

{

Program p = new Program();

// For checked

Console.WriteLine("Checked output value is: {0}", p.Add());

Console.WriteLine("Checked output value is: {0}", p.Mul());

// For Unchecked

Console.WriteLine("Checked output value is: {0}", p.Add_Unchecked());

Console.WriteLine("Checked output value is: {0}", p.Mul_Unchecked());

Console.ReadKey(true);

}

}

}

Output