Repair8 of 14 · about 6 min

Repair: a switch that falls through

A switch jumps to the matching case and then keeps running — through the next case, and the one after that — until it meets a break or the end of the switch. That is called fall-through, and it is deliberate: it is how several labels share one piece of code.

It is also the most common way a switch goes wrong, because a missing break looks like nothing at all.

When you mean to fall through, say so in a comment. Reviewers and compilers both look for it.

Example

switch (c) {
    case 'a':
    case 'e':            /* deliberate: both share the body below */
        vowels++;
        break;
    default:
        others++;
}

Your task

This grader is meant to print one line per score. It prints too much. Fix it without changing the structure — the labels and the messages are all correct.

Stuck?

Explain it

Why is the last default allowed to have no break?

Not graded — this is for you.

Where this goes

Project 4 asks for a command dispatcher built on a switch. This is the failure it will hand you if you forget one break.

#include <stdio.h>

void grade(int score) {
    switch (score / 10) {
        case 10:
        case 9:
            printf("excellent\n");
        case 8:
        case 7:
            printf("good\n");
        case 6:
            printf("pass\n");
        default:
            printf("not yet\n");
    }
}

int main(void) {
    grade(95);
    grade(72);
    grade(64);
    grade(30);
    return 0;
}

Ctrl+Enter checks

This is a teaching runtime for a subset of C, running in your browser on a 32-bit model machine. It reports mistakes a real compiler lets through — reading uninitialised memory, running off an array, signed overflow — and it is not the compiler your project uses.

Press Run to see what your program does, or Check when you think it is right. Everything runs here in your browser.