My friend requested a navigation menu for his code that he has since he didn't really know how to do it, so I had created one for him. I just wanted to get it reviewed since I'm a beginner with C and want to see if there is any way to shorten or improve this.////  main.c//  Oyster Top Up Menu////  Created by JStudent#include <stdio.h>#include <stdlib.h>int main(int argc, const char * argv[]) {    /* Variable Sets */    char firstname[21];    char lastname[21];    int menuselect;    int oystnumber[11];    int oystregnumber[11];    int oystadminnumber = 1621941;    /*****************/    printf(1. Register Oyster Card\n);    printf(2. Login with Oyster Card > );    scanf(%d, &menuselect);        switch(menuselect) {            case 1 :                printf(Please enter your first name: );                scanf(%20s, firstname);                //system(cls);                printf(Please enter your last name: );                scanf(%20s, lastname);                //system(cls);                printf(Enter your 10 Digit Oyster Card Number: );                scanf(%10d, oystregnumber);                break;            case 2 :                printf(Please enter your 10 Digit Oyster Card Number: );                scanf(%10d, oystnumber);                if (oystnumber == oystregnumber) {                    printf(Welcome, %s %s., firstname, lastname);                } else if (oystnumber == oystadminnumber) {                    printf(Welcome, Admin!);                }                break;    }    return 0;}/* Remember to learn how to repeat the switch menu after break; */
Menu Navigations
c