Debugging VB .NET Applications

In this section we will focus on some common issues while debugging our applications and we will take a close look at the Debug Menu Visual Studio .NET provides us. Errors in programming are inevitable. Everyone of us introduce errors while coding. Errors are normally referred to as bugs. The process of going through the code to identify the cause of errors and fixing them is called Debugging.

Types of Errors

Syntax Errors

The most common type of errors, syntax errors, occur when the compiler cannot compile the code. Syntax errors occur when keywords are typed incorrectly or an incorrect construct is parsed. The image below displays a syntax error in the code editor.

Fixing Syntax Errors

VS .NET allows us to easily identify syntax errors. When we build the project, syntax errors are automatically detected and underlined in code. Errors that are detected are also added to the Task List window. You can double-click any error in the Task List window and the cursor will immediately highlight that error in the code window. In most cases this is sufficient to correct the errors.

Run-Time Errors

Run-Time errors occur when the application attempts to perform a task that is not allowed. This includes tasks that are impossible to carry out, such as dividing by zero, etc. When a run-time error occurs, an exception describing the error is thrown.  Exceptions are special classes that are used to communicate error states between different parts of the application. To handle run-time errors, we need to write code (normally, using Try...Catch...Finally) so that they don't halt execution of our application. The image below shows a run time error.

Logical Errors

Logical Errors occur when the application compiles and executes correctly, but does not output the desired results. These are the most difficult types of errors to trace because there might be no indications about the source of the error. The only way to detect and correct logical errors is by feeding test data into the application and analyzing the results. The image below describes a common scenario where logical errors occur.

Assume, the image above performs some calculations for the purpose of taxation. It multiplies three numbers. First number is the hourly wage an employee gets, second number is the number of weeks in a year and third number is the number of hours a week (40 hrs fulltime) the employee works. What happens here is, the code still executes correctly and produces the output but the produced output is not the desired result as the third number in code is 400 instead of 40. The output shown is 249 grand instead of 24 grand. This is a simple scenario where logical errors occur.