Banking system C++

#include <iostream.h>
#include <stdlib.h>
#include <string.h>
#include <dos.h>


//the list of function prototypes

void Deposit();
void Withdraw();
void Query();
void Show();
void Exit();
char Menu();

int acc, dep, with;
int add = dep + with; //this should add both the deposit and withdraw to give total
int sub= dep - with;
//++++++++++++++++++++++++++++++++++++++++++++++++++   +++++++++
int main()
{
char choice;

do{
choice = Menu();
switch(choice)
{
case 'D' : Deposit(); break;
case 'W' :Withdraw();break;
case 'Q' :Query ();break;
case 'S' :Show(); break;
case 'E' :Exit ();break;
default:cout<<"\n\tINVALID ACCOUNT NUMBER ENTERED, PLEASE TRY AGAIN!!!..\n\n\n";

}

}while(choice !='E'); // end of while loop



return 0;
} //This is the end of the main program

//++++++++++++++++++++++++++++++++++++++++++++++++++   ++++++++++++

char Menu()
{
char choice;


cout<<"\tWelcome to Superbank International \n";
cout<<"====================================";
cout<<"\n D Deposit \n ";
cout<<"\n W Withdraw \n";
cout<<"\n Q Query \n";
cout<<"\n S Show all \n";
cout<<"\n E Exit \n";

cout<<"\n\n Option: ";
cin>>choice;


return choice;
}
//+++++++++++++++++++++++++++++++++++++++++++++
void Deposit()
{
system ("cls"); //this will clear the screen


cout<<"Enter the Account Number: ";
cin>>acc;

if ((acc == 25784) ||(acc == 36256)||(acc == 43815) )
{
cout<<"Enter amount to Deposit:$ ";
cin>>dep;
}
else
{
cout<<"\n\n\tSORRY ACCOUNT NUMBER NOT FOUND!!!\n\n";
}
cout<<"\tTRANSACTION APPROVED\n\n";
cout<<"^^^^^^^^^^^^^^^^^^^^^^^^^";
cout<<"\n\nThe Balance on Account " <<acc<< "is $" <<add<<endl;
}
//+++++++++++++++++++++++++++++++++++++++++++++++++
void Withdraw()
{
system ("cls");

cout<<"Enter the Account Number: ";
cin>>acc;

if ((acc == 25784) ||(acc == 36256)||(acc == 43815) )
{
cout<<"Enter amount to Withdraw:$ ";
cin>>with;
}
else
{
cout<<"\n\n\tSORRY ACCOUNT NUMBER NOT FOUND!!!\n\n";
}

cout<<"\tTRANSACTION APPROVED\n\n";
cout<<"^^^^^^^^^^^^^^^^^^^^^^^^^";
cout<<"\n\nThe Balance on Account " <<acc<< "is $" <<sub<<endl;
}
//++++++++++++++++++++++++++++++++++++++++++++++++
void Query()
{
system("cls");
cout<<"some text later";
}
//++++++++++++++++++++++++++++++++++++++++++++++++++   
void Show()
{
system("cls");
cout<<"It has been printed";
}
//+++++++++++++++++++++++++++++++++++++
void Exit()
{
system("cls");
cout<<"\n\n\t\tTHANK YOU, FOR USING Superbank International ......\n\n";
exit(1); // quit the programme
}

    int acc, dep, with;
    int add = dep + with; //this should add both the deposit and withdraw to give total
    int sub= dep - with;
   

   //global declaration
   //added to hold total account value
   int accntbal;
   
   
   //in your Deposit() function after your cin >> dep
   
   accntbal += dep;
   
   
   
   //in your Withdrawal function after your  cin>> with
   
   accnt -= with;