Basics of C#: Checked and Unchecked Conversions

Objective 

In this article, I will discuss about Checked and unchecked keyword and conversions in C#. 

Consider the below code 

Program.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace ConsoleApplication7

{

    class Program

    {

        static void Main(string[] args)

        {

                int number = int.MaxValue;

                number = number + 1;

                Console.WriteLine(number);

                Console.Read();

        }

    }

}

Now, if you see the above code 

1. We are taking maximum integer value in a variable.  And that is 2147483647.
   
   
   
   
2. We are increasing the number by 1. Now here it should get overflow  because an integer variable cannot hold a number greater than  2147483647
   
   
   

So, now data will overflow and truncate during the assignment. 

So, as the output we will get 

 

If you notice above output, number assigned is truncated to -2147483647

It happened because compiler is doing unchecked compilation 

So forcefully do the checked compilation, we will use CHECKED keyword.  Just put all the codes in between checked block 

 

So, now to avoid truncating during overflow assignment, we need to put our code in between Checked block. 

So, modify the above code as below 

Programs.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace ConsoleApplication7

{

    class Program

    {

        static void Main(string[] args)

        {

            checked

            {

                int number = int.MaxValue;

                number = number + 1;

                Console.WriteLine(number);

                Console.Read();

            }

        }

    }

}

Now if you run the above code, you will get the below error. 

 

It shows if the code is in checked block then rather than truncating at overflow, compiler is throwing an exception. 

If we are doing checked compilation then to override that, we can put our code in Unchecked Block 

 

You can change the behavior of compiler from checked to unchecked through command prompt.