Enums

An enum (enumeration) creates a set of named integer constants, useful whenever a variable should only ever hold one of a small, fixed set of values.

#include <stdio.h>

enum Status {
    PENDING,   // 0
    APPROVED,  // 1
    REJECTED   // 2
};

int main(void) {
    enum Status s = APPROVED;
    if (s == APPROVED) {
        printf("Approved!\n");
    }
    return 0;
}

By default, the first member is 0 and each following one increments by 1. You can override this explicitly:

enum HttpStatus {
    OK = 200,
    NOT_FOUND = 404,
    SERVER_ERROR = 500
};

Why not just use plain ints?

You could use #define APPROVED 1, but an enum gives the compiler (and your editor) a real type to check, so passing an unrelated integer where a Status is expected can trigger a warning, and switch statements over an enum can warn you if you forgot to handle a case:

#include <stdio.h>

enum Status { PENDING, APPROVED, REJECTED };

int main(void) {
    enum Status s = APPROVED;
    switch (s) {
        case PENDING:  printf("Waiting...\n"); break;
        case APPROVED: printf("Approved!\n"); break;
        case REJECTED: printf("Rejected.\n"); break;
    }
    return 0;
}

Under the hood, an enum value really is just an int, C has no runtime type safety here, it's purely a naming and readability convenience, but a very useful one.