Program Ekripsi dan Dekripsi c++ tanpa class

#include <cstdlib>
#include <iostream>
#include <string.h>
#define maks 500
using namespace std;
main(){
    char chiper[maks];
    int key,x,a;
    char plain[maks];
    menu:
    cout<<"            Program Ekripsi dan Dekripsi\n";
    cout<<"            ============================\n\n\n\n";
    cout<<"[1] Enkripsi"<<endl;
    cout<<"[2] Dekripsi"<<endl;
    cout<<"Masukkan pilihan anda = ";
    cin>>x;
    system("cls");
    if(x==1){
    cout<<"            Program Ekripsi\n";
    cout<<"            ============================\n\n\n\n";
    cout<<"Masukkan kata : ";
    cin.ignore(); cin.getline(chiper,sizeof(chiper));
    cout<<"Masukkan key : ";
    cin>>key;
    cout<<endl;
    for(int i=0;i<strlen(chiper);i+=1){
    cout<<chiper[i]<<"("<<int(chiper[i])<<") ";
    chiper[i] = (chiper[i]+key)%128;
    }
    cout<<endl;
    for(int i=0;i<strlen(chiper);i+=1){
    cout<<chiper[i];
    }
    for(int i=0;i<strlen(chiper);i+=1){
    plain[i] = (chiper[i]-key)%128;
    chiper[i] = plain[i];
    }
    cout<<"\n\n";
    cout<<"[1] Menu Utama"<<endl;
    cout<<"[2] Keluar"<<endl;
    cout<<"Masukkan pilihan anda = ";
    cin>>a;
    system("cls");
    if(a==1){
        goto menu;
    }
    else if(a==2){
        cout<<"Terima Kasih";
    }
    }
    else if(x==2){
    cout<<"                   Program Dekripsi\n";
    cout<<"            ============================\n\n\n\n";
    cout<<"Masukkan kata : ";
    cin.ignore(); cin.getline(chiper,sizeof(chiper));
    cout<<"Masukkan key : ";
    cin>>key;
    cout<<endl;
    for(int i=0;i<strlen(chiper);i+=1){
    cout<<chiper[i];
    }
    cout<<"\n\n";
    cout<<"[1] Menu Utama"<<endl;
    cout<<"[2] Keluar"<<endl;
    cout<<"Masukkan pilihan anda = ";
    cin>>a;
    system("cls");
    if(a==1){
        goto menu;
    }
    else if(a==2){
        cout<<"Terima Kasih";
    }
    }
return 0;
}