Introduction

Exception handling is handling known or unknown errors from the program. So, when any error occurs then the program should recover gracefully from the error.

In computing and computer programming, exception handling is the process of responding to the occurrence of exceptions – anomalous or exceptional conditions requiring special processing – during the execution of a program.

Wiki

The basic purpose of exception handling is to maintain the normal flow of the program irrespective of errors or exceptions which might occur during the execution of the program.

Error categories

In programming error are categorized in two types:

Compile Time Errors

These errors are those which occur due to syntactical errors like not putting a semi-colon at the end of the statement or missing a curly brace while starting or ending a code block. But such errors are caught by the IDE itself and the programmer is notified about such errors. The code does not run till the time such errors are rectified.

Run-Time Errors

Run time errors are those errors that occur not at the compile-time, but they occur at the runtime. Run-Time Errors are called Exceptions. Hence, we only need to handle the exceptions as Compile-time errors can be handled by IDE itself.

Why exception occurre

There is various reasons for exceptions occurrence

Wrong logic implementation

CLR (Common Language Runtime) cannot check the logic at compile time, it simply checks for the syntax at compile time which everyone should follow.

For example, let’s look at the following code, which is attempting to add up the numbers one to hundred:

using System;

namespace ExceptionExample
{
    public class Program    
    {
        public static void Main()
        {
            var start = 100;
            var end = 1;
            var result = 0;

            for (int i = start; i < end; i++)
            {
                result++;
            }

            Console.WriteLine($"Result: {result}");
            Console.ReadLine();
        }
    }
}

When the code is run, however, it gives an answer of zero. The programme runs OK and didn’t produce any error message or wavy lines. It’s just not the correct answer!

The problem is that we’ve made an error in our logic. The start variable should be 1 and the end variable 100. We’ve got it the other way around, in the code. So, the loop never executes.

Wrong Inputs to run the program

suppose the application requires the user to enter an integer value, however the value supplied is anything but integer. Hence in such a case also the program will terminate abruptly. Consider the following example:

Code for Program class:

using System;

namespace ExceptionExample
{
    public class Program    
    {
        public static void Main()
        {
            Console.WriteLine("Enter a number:");
            var n = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Enter a number:");
            var n1 = Convert.ToInt32(Console.ReadLine());

            var result = n / n1;

            Console.WriteLine($"Result: {result}");
            Console.ReadLine();
        }
    }
}

Now in this program if you enter an integer value the program will run smoothly. But if you provide a string value, you will encounter a “FormatException”.

Connectivity issues

suppose you have written a program to connect to the database and access database information but for some reason database server is offline. Now if you run the program, it will error out as the connection issue.

These are some of the typical runtime errors there are several reasons why runtime errors occur and to run the smooth program we need to handle this run time exceptions.

If you do not handle those exception, then the program can be abruptly terminating on the line where such an error occurs, and remaining line of code will not be executed.

Next post will explain about how to implement exception , nested try-catch blocks and creating custom exception’s

List of exception

Here is complete the list of Exceptions:

In the next post Exception Handling C# – Part II, will cover the way to handle the exception, multiple exception handling, and writing custom exception.