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Q: Why are there so many software bugs?
A:
There are bugs in software because of unclear requirements, software complexity, programming errors, changes in requirements, errors made in bug tracking, time pressure, poorly documented code and/or bugs in tools used in software development.
There are unclear software requirements when there is miscommunication as to what the software should or shouldn't do.
As to software complexity, all of the followings contribute to the exponential growth in software and system complexity: Windows interfaces, client-server and distributed applications, data communications, enormous relational databases, and the sheer size of applications.
Programming errors occur because programmers and software engineers, like everyone else, can make mistakes.
As to changing requirements, in some fast-changing business environments, continuously modified requirements are a fact of life. Sometimes customers do not understand the effects of changes, or understand them but request them anyway. The changes require redesign of the software, rescheduling of resources, and some of the work already completed have to be redone or discarded. Hardware requirements, too, can be effected.
Bug tracking, too, can result in errors because the complexity of keeping track of changes.
Time pressures can cause problems, because scheduling of software projects is not easy; it often requires a lot of guesswork; and when deadlines loom and the crunch comes, mistakes will be made.
Code documentation is tough to maintain. It's also tough to modify code that is poorly documented. The results are bugs. Sometimes there is no incentive for programmers and software engineers to document their code and write clearly documented, understandable code. Sometimes developers get kudos for quickly turning out code, or programmers feel they don't have job security, if everyone can understand the code they write, or they believe if the code was hard to write, it should be hard to read.
Software development tools , including visual tools, class libraries, compilers, scripting tools, can introduce their own bugs. Other times the tools are poorly documented, which can create additional bugs.
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