---
title: "Phases of introduction of bugs in software"
subject: "Instrumentation II"
chapter: 9
key: "semester_5/instrumentation_ii:bugs-introduction"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/bugs-introduction
site: BCT Engineering
---

# Phases of introduction of bugs in software

Instrumentation II · Chapter 9: Software For Instrumentation And Control Applications

- Asked in: 2074 Chaitra, 5 marks; 2069 Chaitra, 4 marks (asked 2 times)
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/bugs-introduction
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-9

## Question

Explain the different phases of introduction of bugs in software.

## Short answer

Software bugs originate in requirements (missing, wrong), design (faulty logic, interfaces), coding (syntax, logic, memory), testing (insufficient cases, regression), integration (mismatches), and maintenance (patches). Cost rises sharply if found late.

## Answer

A software **bug** is an error, flaw or fault in a program that makes it produce wrong or unexpected results. Bugs can be introduced in any phase of the software life cycle:

1. **Requirements phase:** missing, incomplete, ambiguous or wrong requirements; misunderstanding between customer and developers; later changes of the requirements. These are the most costly bugs because the whole product is built wrongly.
2. **Design phase:** wrong architecture, poor algorithms, faulty logic, ignoring timing or interface issues, poor module partitioning and wrong data structures.
3. **Coding (implementation) phase:** syntax and logic errors, wrong variable use, uninitialised variables, off-by-one errors, array overflow, memory leaks, pointer errors, wrong data types, inconsistent interfaces, and failure to follow the standards.
4. **Testing phase:** wrong or insufficient test cases, incorrect test environment and fixes that add new bugs (regression).
5. **Integration and installation phase:** interface mismatches between modules, wrong configuration, version conflicts and environment differences (hardware/OS).
6. **Maintenance phase:** modifications and patches that introduce new bugs or break working parts; poor documentation.

The cost of removing a bug rises sharply the later it is found, so reviews and testing at each phase are important.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why are requirements-phase bugs the most costly?
   A. They are easy to fix
   B. The whole product is built wrongly
   C. They only affect documentation
   D. They appear in testing only
   Answer: B. Wrong or missing requirements propagate into all later phases. (Key point: Requirements bugs)

2. Which is a coding-phase bug?
   A. Ambiguous requirement
   B. Off-by-one error or uninitialised variable
   C. Wrong architecture
   D. Version conflict at installation
   Answer: B. Syntax and logic errors such as off-by-one and uninitialised variables arise during coding. (Key point: Coding bugs)

3. How are bugs introduced during maintenance?
   A. Patches and modifications break working parts
   B. Requirements gathering
   C. Initial design
   D. None
   Answer: A. Changes and poor documentation introduce new faults. (Key point: Maintenance bugs)

4. How does the cost of removing a bug change with time of discovery?
   A. It falls
   B. It is constant
   C. It rises sharply the later it is found
   D. It is zero in testing
   Answer: C. Reviews and testing at each phase catch bugs early. (Key point: Cost of bug removal)

## Related in Instrumentation II

- [Software bugs and testing techniques](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Abug-types-testing) — Instrumentation II, chapter 9, asked 2×
- [Software maintenance and fixing common bugs](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-maintenance-bugs) — Instrumentation II, chapter 9
- [Nature of bugs and preventive steps](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Abugs-prevent) — Instrumentation II, chapter 9, asked 2×

## Related in other subjects

- [Proposal to start a software company](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Aproposal-software-company-ministry) — Communication English, chapter 6