A software bug is a problem, error, fault, or failure in the computer program that produces an unexpected result or uncharacteristic behavior. Debugging is the process of identifying such errors and rectifying them to ensure proper running of the system. Since 1950s, some systems are designed to rectify such bugs automatically during operations. Many bugs arise from mistakes and errors created within the source code or the design of the program.
Many bugs are a result of mistakes and errors made in either the program’s source code or the design, or in the components an operating systems used by these kinds of programs. Few bugs are caused by compilers producing the incorrect code. Programs with many bugs that interfere with the functionality is said to be buggy. Bugs trigger errors that can have ripple effects. They may have subtle effects or crash the program or freeze the device. Other bugs might allow a malicious user to bypass access controls to obtain unauthorized privileges and information.
Software bugs have also been linked to disasters. For example, in the 1980s, multiple patient deaths received from the Therac-25 radiation therapy machine were solely attributed to bugs in code that controlled the machine. Similarly, in June 1994, 29 people were killed when a Royal Air Force Chinook helicopter crashed into the Mull of Kintyre; initially dismissed as a pilot error, an investigation convince a House of Lords inquest that the crash could be attributed to a software bug in the aircraft’s engine-control computer.
Bugs are of multiple types, and it is important to understand its nature, its implications and the cause to process it better. Bugs can be introduced as a consequence of unfinished or wrong requirements or due to human data entry issues.
The functionality of the program is the way or process the program is intended to behave. Programs or software have functionality bugs when it does not behave or produce the desired result.
For example, while closing a new unsaved word document program, the ‘Cancel’ button should close and none of the changes made to the program should be saved, i.e., no document should be created. If the button is not clickable, then it is a functionality error.
Communication bugs are those bugs that occur in the communication from software to the end-user. Something that the user should know in order to use the software or program should be prominently displayed on the screen; the unavailability of such data could cause the user to improperly use the software and create problems.
For example, if there would be no help section or drop down menu provided, features not documented in the help section, or buttons and options performing functions other than their necessary functions; such as in a word document program, the ‘Cancel’ prompting the user to save the changes that have been made to the program.
Missing Command Bugs
Missing Command Bugs are bugs that occur when a command that is expected is missing or blocked from functioning. This would cause an error in functionality or prevent the result from being that which is expected as a crucial part of code is not present.
For example, in the word document program, if the functionality to ‘Save’ the file is not available and the changes made to the program cannot be saved as a new file, this is a missing command error as the ‘Save’ command is missing.
Syntactic Bugs are misspelled word or grammatically incorrect phrases that are quite evident while testing the software GUI. This does not refer to the syntactical errors in the code; the compiler warns the developer about any syntax errors have been spotted in the code.
For example, in the word document program, the ‘Save’ button displays ‘Sve’ or the ‘Cancel’ button displays ‘Cacnel’; these would constitute as syntactical errors.
Error Handling Bugs
A bug that occurs while the user interacts with the software needs to be handled in a clear and efficient manner; if not, such is called an Error Handling Bug. When possible, further steps should be listed for the user to follow and implement. An error message that gives no indication of the problem is considered an Error Handling Bug.
For example, in the word document program, if the software requires the user to fill out certain mandatory fields while saving the changes made to the program, clear validation messages should prompt the user as to the necessary actions they must undertake.
A calculation bug could be due to bad logic implemented, incorrect formula used, data type mismatch in the available fields, coding errors while writing the program, function call issues that prohibit proper space handling, etc.
For example, the 1999 NASA Mars orbiter crashed on arrival due to a calculation bug in the system; one of the subcontractors has used English units instead of the expected metric system causing the thrusters to function improperly.
Control Flow Bugs
The control flow of a program describes the procedure of performance and states the sequence of function to be used for proper functioning. Bugs that cause the program to stray from the normal sequence of function calls are called Control Flow Bugs.
For example, in the word document program, when the user saves the program in one folder, but the folder get saved in another location due to an error in the address handling of the system.
Bug identification, categorization, documentation and eventual removal are part of Quality Control activities. However, prevention is better than cure. The importance of Software Quality Assurance is to establish monitoring and inspection protocols are every part of the Software Development Life Cycle (SDLC), with the aim being to detect bugs as early as on possible because the costs to find and fix the bugs dramatically increase as the software development progresses. Thus, identifying bugs early on is essential.