<P> The software industry has put much effort into reducing bug counts . These include: </P> <P> Bugs usually appear when the programmer makes a logic error . Various innovations in programming style and defensive programming are designed to make these bugs less likely, or easier to spot . Some typos, especially of symbols or logical / mathematical operators, allow the program to operate incorrectly, while others such as a missing symbol or misspelled name may prevent the program from operating . Compiled languages can reveal some typos when the source code is compiled . </P> <P> Several schemes assist managing programmer activity so that fewer bugs are produced . Software engineering (which addresses software design issues as well) applies many techniques to prevent defects . For example, formal program specifications state the exact behavior of programs so that design bugs may be eliminated . Unfortunately, formal specifications are impractical for anything but the shortest programs, because of problems of combinatorial explosion and indeterminacy . </P> <P> Unit testing involves writing a test for every function (unit) that a program is to perform . </P>

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