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Editorial Team
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Asked: 2026-06-11T19:22:23+00:00

Two days ago i attended an interview.I had been asked a question and i

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Two days ago i attended an interview.I had been asked a question and i am still finding answer.The Question Was tell me the test cases of atof(const char *str) function in c.I told him various test cases like

  1. I have to check the given string should contain only numeric.
  2. Given string contain one decimal point.
  3. it should not overflow after conversion.
  4. string should not be null.

but interviewer was not satisfied and asking for give me the answer in structured format.now my question is how to represent this answer in structure format so that in future i could not make same mistake.

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  1. Editorial Team

    I’m not sure what the interviewer means by “structured format”, but I would do this by writing down the BNF syntax for floating point numbers (the C language specifies them), and then presenting test cases that test for each path through the syntax. Your cases notably do not cover the sign or exponent, and the number need not contain a decimal point.

    A structural approach breaks the problem down into subproblems. Syntax is one subproblem, and the syntax chart or BNF provides a natural way to break that down into subproblems. An additional subproblem is boundary conditions … there should be test cases for the minimum (> 0) and maximum valid values. There should also be test cases for handling of invalid inputs, but as lundin noted in a comment, that’s impossible for atof as the behavior for invalid inputs is undefined.

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