C# - Difference Between IS and AS Keyword

The method used to change one data type to another is called type casting. If the prior data type is incompatible with the new data type while type casting one data type to another, we get an exception. We have the IS and AS operators in C# for safe type casting to prevent this exception. Let's learn how to use them both.

1. IS Operator

The "is" operator is used to determine check whether two objects are of the same type or not. The is keyword returns true if the given object is of the same type.

Example

you might use IS to check if an object is a string before performing certain operations on it.

using System;
using System.Text;

namespace FirstProgram
{
    class Program
    {
        static void Main(string[] args)
        {
            object obj = "TutorialsTrend";
            if (obj is string)
            {
                Console.WriteLine(obj.ToString().ToUpper());
            }
        }
    }    
}

Output

2. AS Operator

The "as" operator is used to perform safe type conversions. It is used to convert the object of one type to other. It attempts to cast an object to a specified type, and if the cast is successful, returns the object of the specified type. If the cast fails, it returns null.

Example

you might use AS to convert an object to a string:

using System;
using System.Text;

namespace FirstProgram
{
    class Program
    {
        static void Main(string[] args)
        {
            object obj = "TutorialsTrend";
            string str = obj as string;
            if (str != null)
            {
                Console.WriteLine(obj.ToString().ToUpper());
            }
        }
    }    
}

Output

In this example, AS attempts to cast the object "obj" to a string. If the cast is successful, the resulting string is assigned to the variable "str". If the cast fails (e.g. if "obj" is not a string), "str" is set to null.

When to Use

• Use is when you only need to check the type of an object and perform some logic based on that.
• Use as when you need to attempt to cast an object and handle the failure case without exceptions.

Difference between IS and AS Keyword in C#