enum: Named Choices

Say a traffic light can be red, yellow or green. You could use 0, 1 and 2 – but who remembers which is which? An enum (enumeration) gives each number a name:

#include <stdio.h>

enum Light { RED, YELLOW, GREEN };

int main() {
    enum Light now = GREEN;
    if (now == GREEN) {
        printf("Go!\n");
    }
    printf("GREEN is really the number %d\n", now);
    return 0;
}

Output

Go!
GREEN is really the number 2

C numbers the names for you, starting at 0: RED is 0, YELLOW is 1, GREEN is 2.

enum and switch

Enums and switch fit together perfectly:

#include <stdio.h>

typedef enum { NORTH, EAST, SOUTH, WEST } Direction;

void describe(Direction d) {
    switch (d) {
        case NORTH: printf("Up\n"); break;
        case EAST:  printf("Right\n"); break;
        case SOUTH: printf("Down\n"); break;
        case WEST:  printf("Left\n"); break;
    }
}

int main() {
    describe(SOUTH);
    describe(EAST);
    return 0;
}

Output

Down
Right

Choosing the numbers

You can pick the numbers yourself. The ones after continue counting up:

#include <stdio.h>

enum Month { JAN = 1, FEB, MAR, APR };

int main() {
    printf("%d %d %d\n", JAN, FEB, APR);
    return 0;
}

Output

1 2 4

Remember: Use an enum whenever a value can only be one of a few named choices.