does this pass all cases
* 
 * Change the filename for the profile pic of the given user. 
 * 
 * Return: 
 *   - 0 on success. 
 *   - 1 if the file does not exist or cannot be opened. 
 *   - 2 if the filename is too long. 
 */  
int update_pic(User *user, const char *filename) {  
    if(strlen(filename) > 31){
        return 2;
    }
    FILE *picture;
    picture = fopen(filename, "r");

    if(picture == NULL){
        // fprintf(stdout, "fail");
        return 1;
    }else {
        strcpy(user-> profile_pic, filename);
        // fprintf(stdout, "success");
        return 0;
    }
}  
  