vehicle maintenance program question

the following is a console vehicle maintenance program. We cannot seem to get the edit function working correctly: when we wish to delete a vehicle it does not work. Try out the program and see if it works for you. I would appreciate any advice...thanx in advanx

Code:

---

//============================================================================
// Vehicle Maintenance Tracking Application
// -----------------------------------------
//
// Application Overview:
// This application allows the user to input up to 20 different vehicles that will be tracked.
// Each Vehicle will have the data entered.......
//
//

//==============================================================================

// Header Files
#include "stdafx.h"
#include <iostream>
#include <string>
#include <iomanip>

// Namespace
using namespace std;

// Structs
struct vehicleType
{
        int number;
        int mileage;
        string plate;
        string vin;
        string model;
};

// Prototypes
void mainMenu(int& parUserChoice);
void initVehicles(vehicleType parVehicles[]);
void QuickCheck(vehicleType parVehicles[]);
void addVehicle(vehicleType parVehicles[]);
void EditVehicle(vehicleType parVehicles[]);
void ListVehicles(vehicleType parVehicles[]);

// Global Variables
char x;
int main (void)
{
        // Local Variable Declaration
        int userChoice = 0; // User main menu selection
        vehicleType vehicles[20]; // Create 20 element struct
       
        initVehicles(vehicles);
        do
        {
                mainMenu(userChoice);
                switch (userChoice)
                {
                case 0:
                        //Exit
                        break;
                case 1:
                        addVehicle(vehicles);
                        break;
                case 2:
                        EditVehicle(vehicles); //call EditVehicle function
                        break;
                case 3:
                        QuickCheck(vehicles);//call QuickCheck function
                        break;
                case 4:
                        ListVehicles(vehicles); //call Reports function
                        system("PAUSE");
                        break;
                }
        }while (userChoice != 0);
}

void mainMenu(int& parUserChoice)
{ // Begin mainMenu
        do  // Displays menu until user chooses to quit the program
        {        // Begin do loop
                // Clear Screen
                system("cls");

                // List Main Menu
                cout << " Main Menu" << endl;
                cout << "===========" << endl;
                cout << "1 - Enter New" << endl;
                cout << "2 - Edit" << endl;
                cout << "3 - Quick Check" << endl;
                cout << "4 - Display Report" << endl;
                cout << "0 - Exit" << endl;
                cout << "Enter your selection(1-4, 0 to exit): ";
                cin >> parUserChoice;
        } while (parUserChoice > 4 || parUserChoice <0); // Continues until user enters a valid selection
} // End mainMenu

void addVehicle(vehicleType parVehicles[])
{        // Begin addVehicle
        bool found = false;

        for (int counter = 0;counter<20;counter++) // Loop to count through vehicle records
        {
                if (parVehicles[counter].number == 0) // Checks whether data record exists
                {
                        parVehicles[counter].number = counter + 1;
                        cout << "Enter Model: ";
                        cin >> parVehicles[counter].model;
                        cout << "Enter VIN: ";
                        cin >> parVehicles[counter].vin;
                        cout << "Enter Plate Number: ";
                        cin >> parVehicles[counter].plate;
                        cout << "Enter Mileage (Whole numbers only): ";
                        cin >> parVehicles[counter].mileage;
                       

                    counter = 20;
                        found = true;
                }
        }

        if (!found) // Used if all struct elements have data in them
        {
                cout << "Vehicle capacity is full" << endl;
                system("pause");
        }
}


void initVehicles(vehicleType parVehicles[])
{
        // Init all vehicle numbers to 0
        for (int counter = 0;counter < 20;counter++)
        {
                parVehicles[counter].number=0;
        }
}

void EditVehicle(vehicleType parVehicles[])
{        // Begin EditVehicle()
        int EditSelect = 0;        // User selection of which vehicle attribute to edit
        int VehicleSelect = 0; // User selection of which vehicle to edit

        if(parVehicles[0].number == 0) // Checks to see if there is at least one record in the system
        {
                cout << "There are no vehicles in the database to edit.";
                system("PAUSE");
        }
        else // Executed if there is at least one vehicle in the system
        {
                cout << "Which vehicle would you like to edit?" << endl << endl;
                ListVehicles(parVehicles);
                cout << "Please make your selection (1-20) and hit Enter:";
                cin >> VehicleSelect;
                system("cls");
                cout << "What would you like to edit on the vehicle?" << endl;
                cout << "0 - Nothing/Exit Without Changes" << endl;
                cout << "1 - Model" << endl;
                cout << "2 - VIN" << endl;
                cout << "3 - License Plate" << endl;
                cout << "4 - Mileage" << endl;
                cout << "5 - Remove Vehicle" << endl;
                cin >> EditSelect;
               
                switch(EditSelect) // User selection of which vehicle item to edit
                {
                case 0:
                        break; // Quit Edit
                case 1:
                        cout << "Old Model: " << parVehicles[VehicleSelect-1].model << "\tNew Model: ";
                        cin >> parVehicles[VehicleSelect-1].model;
                        break;
                case 2:
                        cout << "Old VIN: " << parVehicles[VehicleSelect-1].vin << "\tNew VIN: ";
                        cin >> parVehicles[VehicleSelect-1].vin;
                        break;
                case 3:
                        cout << "Old Plate: " << parVehicles[VehicleSelect-1].plate << "\tNew Plate: ";
                        cin >> parVehicles[VehicleSelect-1].plate;
                        break;
                case 4:
                        cout << "Old Mileage: " << parVehicles[VehicleSelect-1].mileage << "\tNew Mileage: ";
                        cin >> parVehicles[VehicleSelect-1].mileage;
                        break;
                case 5:
                        cout << "Deleting Vehicle: " << parVehicles[VehicleSelect-1].model << " ";
                        parVehicles[VehicleSelect-1].number = NULL;
                        //parVehicles[VehicleSelect-1].model = " ";
                        //parVehicles[VehicleSelect-1].vin = " ";
                        //parVehicles[VehicleSelect-1].plate = " ";
                        //parVehicles[VehicleSelect-1].mileage = 0;
                        system("cls");
                        ListVehicles(parVehicles);
                        system("PAUSE");
                        break;



                } // End switch statement
        }        // End else statement
}        // End EditVehicle()

void ListVehicles(vehicleType parVehicles[])
{
        if(parVehicles[0].number == 0)
        {
                cout << "You have not entered any vehicles in the database.";
                system("PAUSE");
        }
        else
        {
                cout << "Number\tModel\tVIN\tPlate\tMileage" << endl << endl;
                for(int a=0; a<20; a++)
                {        // Begin for loop
                        if(parVehicles[a].number == 0)
                        {        // Begin if statement
                                cout << a+1 << "\tEmpty Record" << endl;        // Prints "Empty Record if a structure element does not contain info
                        }        // End if statement
                        else // Executes if there is at least one vehicle record in the system
                        {        // Begin else statement
                                cout << parVehicles[a].number;
                                cout << "\t" << parVehicles[a].model;
                                cout << "\t" << parVehicles[a].vin;
                                cout << "\t" << parVehicles[a].plate;
                                cout << "\t" << parVehicles[a].mileage << endl;
                        }        // End else statement
                }        // End for loop
        }        // End else statement
}        // End ListVehicles function

void QuickCheck(vehicleType parVehicles[])
{
       
        int a = 0;
        int status = 0;
                cout << "Which vehicle would you like to check?" << endl << endl;
                ListVehicles(parVehicles);
                cout << "Please make your selection (1-20) and hit Enter:";
                cin >> a;
                a = a -1;
                system("cls");

if((parVehicles[a].mileage >= 45000) && (parVehicles[a].mileage < 50000))
{
cout << "Your vehicle will require a 50,000 mile checkup soon.\n";
status = 1;
}
else if (parVehicles[a].mileage >=50000)
{
cout << "The vehicle you have selected is due for a 50,000 mile checkup.\n";
status = 1;
}
 
if((parVehicles[a].mileage >= 25000) && (parVehicles[a].mileage < 30000))
{
cout << "Your vehicle will require a new air filter soon.\n";
status = 1;
}
else if (parVehicles[a].mileage >=30000)
{
cout << "The vehicle you have selected is due for a new air filter.\n";
status = 1;
}

if((parVehicles[a].mileage >= 70000) && (parVehicles[a].mileage < 75000))
{
cout << "Your vehicle will require a 50,000 mile checkup soon.\n";
status = 1;
}
else if (parVehicles[a].mileage >=75000)
{
cout << "The vehicle you have selected is due for transmission checkup.\n";
status = 1;
}

if (status == 0)
  cout << "Your vehicle is currently up to date with maintenance.\n";

system("PAUSE");
}

---

What does it say when you try to delete the vehicle?

If I enter 1 vehicle into it, and then delete that then it states that there are no vehicles in the database, which it should I assume. When I enter 2 or more, it deletes them and they don't appear in the databases anymore, which I assume it should do also.