using arrays in a special way

main.c

#include <stdio.h>

void add(int a, int b) {
    printf("%d\n", a + b);
}

void sub(int a, int b) {
    printf("%d\n", a - b);
}

void mul(int a, int b) {
    printf("%d\n", a * b);
}

void div(int a, int b) {
    printf("%d\n", a / b);
}

enum Action {
    Add,
    Sub,
    Mul,
    Div,
    LastAction
};

static void (*perform[LastAction])(int a, int b) = {
    [Add] = add,
    [Sub] = sub,
    [Mul] = mul,
    [Div] = div,
};

int main() {
    int n, a, b;

    printf("0 for add\n1 for sub\n2 for mul\n3 for div\n");

    while (1) {
        printf("Action: ");
        scanf("%d", &n);

        printf("Enter 1st num: ");
        scanf("%d", &a);

        printf("Enter 2nd num: ");
        scanf("%d", &b);

        if (perform[n]) perform[n](a, b);
        else printf("Invalid action\n");
    }
}