A better alternative to using a long series of "if/else if" statements in C?

Question

Originally I used switch/case, but the condition had to be a constant value that the variable would match, versus a boolean of whether the variable was within the range.

Instead, I have this monstrosity:

    if ( data[y] > 91 ) {
       grades[9] = grades[9] + 1;
    }
    else if ( data[y] > 88 && data[y] < 92 ) {
        grades[8] = grades[8] + 1;
    }
    else if ( data[y] > 84 && data[y] < 89 ) {
        grades[7] = grades[7] + 1;
    }
    else if ( data[y] > 81 && data[y] < 85) {
        grades[6] = grades[6] + 1;
    }
    else if ( data[y] > 79 && data[y] < 82) {
        grades[5] = grades[5] + 1;
    }
    else if ( data[y] > 74 && data[y] < 79 ) {
        grades[4] = grades[4] + 1;
    }
    else if ( data[y] > 71 && data[y] < 75 ) {
        grades[3] = grades[3] + 1;
    }
    else if ( data[y] > 68 && data[y] < 72 ) {
        grades[2] = grades[2] + 1;
    }
    else if ( data[y] > 59 && data[y] < 69 ) {
        grades[1] = grades[1] + 1;
    else {
        //data[y] < 60:
        grades[0] = grades[0] + 1;
    }

Does anybody know a nicer way to handle this block of code, since my switch/case idea can't apply? Surely there has to be a better way to do this.

Answer 1

The most obvious to shorten your code is to get rid of the unnecessary second tests:

if      (data[y] >= 92) ++grades[9];
else if (data[y] >= 89) ++grades[8];
else if (data[y] >= 85) ++grades[7];
else if (data[y] >= 82) ++grades[6];
else if (data[y] >= 80) ++grades[5];
else if (data[y] >= 75) ++grades[4];
else if (data[y] >= 72) ++grades[3];
else if (data[y] >= 69) ++grades[2];
else if (data[y] >= 60) ++grades[1];
else                    ++grades[0];

Answer 2

This seems like a sensible data-driven approach:

int grade_cutoff[] = { 59, 68, 71, 74, 79, 81, 84, 88, 91, INT_MAX };
int grade_bucket;

for (grade_bucket = 0; data[y] > grade_cutoff[grade_bucket]; grade_bucket++) {
  /* nothing */
}

grades[grade_bucket]++;

Answer 3

Use a loop. You'll also need an array of the minimum data value for each grade. Here's some untested code as an example:

for (int i = 9; i >= 0; i--)
{
    if (data[y] >= minDataValueForGrade[i])
    {
        grades[i]++;
        break;
    }
}

It's short, easy to read, and makes it really easy to change the values that correspond to each grade.