int make_friends(const char *name1, const char *name2, User *head) {

    User *user1;
    User *user2;
    
    // Check if name1 is in list
    user1 = find_user(name1, head);
    if (!user1){
        return 4;
    }

    // Check if name2 is in list
    user2 = find_user(name2, head);
    if (!user2){
        return 4;
    }
    
     //Check if the same user is passed in twice.
    if (name1 == name2){
        return 3;
    }

    // Then, name1 and name2 are in the list, check if users have max friend size.
    int len1 = list_length(user1->friends);
    int len2 = list_length(user2->friends);

    if (len1 >= MAX_FRIENDS ||  len2 >= MAX_FRIENDS){
        return 2;
    }

    // Then, check if name1 and name2 are already friends. 
    for (int i = 0; i < MAX_FRIENDS; i++){
        if ((user1->friends)[i] != NULL && strcmp((user1->friends)[i]->name, name2)){
            return 1;
        }
    }

    // Then, all conditions are met. Add the new friends to both lists.

    for (int i = 0; i < MAX_FRIENDS; i++){
        if (user1->friends[i] == NULL){
            user1->friends[i] = user2;
            break;
        }
    }
    
    for (int i = 0; i < MAX_FRIENDS; i++){
        if (user2->friends[i] == NULL){
            user2->friends[i] = user1;
            break;
        }
    }

    return 0;
}
Add user1 to user2's friends array and user 2 to user 1's friends array.