#include <stddef.h>
#include <stdio.h>
#include <string.h>

// typedef function pointer
typedef void logf(size_t bytes, const char src[static bytes + 1]);

void echo(size_t n, const char src[static n + 1]) {
    printf("forward: %s\n", src);
}

void rev(size_t bytes, const char src[static bytes + 1]) {
    printf("backward: ");
    for (size_t i = strlen(src); i > 0; i--) {
        printf("%c", src[i]);
    }
    printf("\n");
}

int main() {
    logf *func[2] = {
        [0] = echo,
        [1] = rev};
    int e;
    printf("Echo or Rev: 0 or 1: ");
    scanf("%d", &e);
    const char *s = "Hello, World";
    if (e >= 0 && e < 2)
        func[e](strlen(s), s);
    else
        puts("Invalid choice.");

    return 0;
}