Question

Quick question, I’m writing a Grade letter program using only switch statements. With if statements I can easily use <, or > to designate a certain range. If the user inputs a number such as 93 I would have to list all the cases from 99-90 which is too redundant. I already wrote the program and it works fine, but I want to get away from bad code. Is there a more reasonable way to write this without listing multiple cases? Hope this makes sense…

Answer 1

You wouldn’t want to use a switch statement to determine where a value falls in a set of ranges.

If you want to generalize a bit, and avoid multiple if/else statements with hard coded conditions, you could create a map. i.e. you are essentially mapping a set of integers to a set of grades.

Below is a simple example that uses a table lookup to map scores to grades. You could also create a closed mathematical formula that maps scores to grades, and just compute the grade directly from the score, instead of looking it up via a table. e.g. f(x) = floor(2*(x-50)/20) would map scores from [0,100] into integer grades in the range [0, 5]

typedef struct
{
    int rangeLow;
    char grade;
} RangeToGradeMap;

RangeToGradeMap[] scoreToGradeMapping =
{
    { 90, 'A' }
    { 85, 'B' },
    { 70, 'C' },
    { 60, 'D' },
    { 0,  'F' },
};

char GradeLookup(int score)
{
    size_t N = sizeof(scoreToGradeMapping)/sizeof(RangeToGradeMap);

    for (size_t i = 0; i < N; ++i)
    {
        if (score >= scoreToGradeMapping[i].rangeLow)
        {
            return scoreToGradeMapping[i].grade;
        }
    }

    // If we got here, there was an error - we didn't find the range

    return '?';
}

int main(int argc, char** argv)
{
    char grade = GradeLookup(87);

    return 0;
}