C# Throw exceptions

In C#, exceptions are thrown when something goes wrong during the execution of a program. Throwing exceptions is a way of signaling that an error has occurred, and it can be used to interrupt the normal flow of the program.

Syntax


throw new Exception("Error message here");

Types of Exceptions

C# provides many types of Exceptions

System.Exception: The base class for all exceptions.
ArgumentNullException: Thrown when a method receives a null argument that is not allowed.
ArgumentOutOfRangeException: Thrown when an argument is outside the allowed range.
InvalidOperationException: Thrown when an operation is not valid due to the current state.
FileNotFoundException: Thrown when an attempt to access a file that does not exist is made.

Throwing an exception when a method argument is invalid

In this example, we will throw an exception if the parameter provided to a method is invalid (for example, a negative number when a positive one is expected).


using System;

class MyProgram
{
    static void Main()
    {
        try
        {
            ValidateAge(-21);  // Invalid age
        }
        catch (ArgumentOutOfRangeException ex)
        {
            Console.WriteLine($"Caught exception: {ex.Message}");
        }
    }

    static void ValidateAge(int age)
    {
        if (age < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(age), "Age cannot be negative.");
        }

        Console.WriteLine("Age is valid.");
    }
}

Output:

Caught exception: Age cannot be negative.
Parameter name: age

Throwing an exception for a null value (ArgumentNullException)

we throw an ArgumentNullException if the user provides a null value for a required argument.


using System;

class MyProgram
{
    static void Main()
    {
        try
        {
            DisplayName(null);  // Invalid name (null)
        }
        catch (ArgumentNullException ex)
        {
            Console.WriteLine($"Caught exception: {ex.Message}");
        }
    }

    static void DisplayName(string name)
    {
        if (name == null)
        {
            throw new ArgumentNullException(nameof(name), "Employee Name cannot be null.");
        }

        Console.WriteLine($"Employee name: {name}");
    }
}

Output:

Caught exception: Employee Name cannot be null.
Parameter name: name

Throwing a custom exception

We can create own exception classes by inheriting from the Exception base class.

Example:


using System;

class CustomException : Exception
{
    public CustomException(string message) : base(message) { }
}

class MyProgram
{
    static void Main()
    {
        try
        {
            throw new CustomException("This is a custom exception.");
        }
        catch (CustomException ex)
        {
            Console.WriteLine($"Caught custom exception: {ex.Message}");
        }
    }
}

Output:

Caught custom exception: This is a custom exception.