C++ – Boundary Conditions for Testing

c

Ok so in a programming test I was given the following question.

Question 1 (1 mark)

Spot the potential bug in this section of code:

void Class::Update( float dt )
{
    totalTime += dt;
    if( totalTime == 3.0f )
    {
        // Do state change
        m_State++;
    }
}

The multiple choice answers for this question were.

a) It has a constant floating point number where it should have a named constant variable

b) It may not change state with only an equality test

c) You don't know what state you are changing to

d) The class is named poorly

I wrongly answered this with answer C.

I eventually received feedback on the answers and the feedback for this question was

Correct answer is a. This is about understanding correct boundary conditions for tests. The other answers are arguably valid points, but do not indicate a potential bug in the code.

My question here is, what does this have to do with boundary conditions? My understanding of boundary conditions is checking that a value is within a certain range, which isn't the case here. Upon looking over the question, in my opinion, B should be the correct answer when considering the accuracy issues of using floating point values.

Best Answer

I think the test question is ambiguously vague.

The problem, of course, is that you're comparing a floating-point number with something (the type of what is being compared is not specified), whereas comparing within a given range (an epsilon) is more appropriate, because comparing floating point numbers with == is unreliable.

Whether the floating point number is being compared to a "named constant" or not is an irrelevant detail.

Another choice example of how test questions created by academics without field experience generally suck.

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