how to add a space in the string greeting
int main(int argc, char **argv) {
    if (argc != 3) {
        fprintf(stderr, "Usage: greeting message name\n");
        return 1;
    }
    char greeting[20];
    char *name = argv[2];

    // Your code goes here

    int length = strlen(argv[1]);
    strncpy(greeting, argv[1], length);

    strcat(greeting, " ");

    strncat(greeting, name, 20 - strlen(greeting));

    printf("%s\n", greeting);
    return 0;
}