(Circular) Queues : Implementation Using Array

/* Copyright (C) 2007 Ankur Banerjee. This program is free software: you can redistribute it and / or modify it under the terms of the GNU General Public License as published by the Free Software Foundation version 3 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. For a copy of the GNU General Public License see http://www.gnu.org/licenses/gpl.html /

/ Array implementation of a Circular Queue /

#include <iostream.h>
#include <conio.h>
#include <process.h>

void main()
{
clrscr();
const int max = 5;
int ch, n, front = -1, rear = -1, q[max], i;
char choice;
do
{
clrscr();
cout<<endl<<“Program Menu”
<<endl<<“1. Insert new element”
<<endl<<“2. Delete an element”
<<endl<<“3. Show list”
<<endl<<“4. Exit”
<<endl<<“Enter your choice: “;
cin>>ch;
switch(ch)
{
case 1 : clrscr();
if (front == (rear + 1) % max)
cout<<endl<<“Queue overflow! Insertion not possible!”;
else if (front == -1 && rear == -1)
{
front = 0;
rear = 0;
cout<<endl<<“Enter number to be inserted: “;
cin>>n;
q[front] = n;
}
else
{
rear = (rear + 1) % max;
cout<<endl<<“Enter number to be inserted: “;
cin>>n;
q[rear] = n;
}
break;
case 2 : clrscr();
if (front == -1 && rear == -1)
cout<<endl<<“Queue does not exist!”;
else if (rear == 0 && front == 0)
{
n = q[front];
rear = -1;
front = -1;
cout<<endl<<“Deleted data item: “
<<n<<endl;
}
else
{
n = q[front];
front = (front + 1) % max;
cout<<endl<<“Deleted data item: “
<<n<<endl;
}
break;
case 3 : clrscr();
if (front == -1 && rear == -1)
cout<<endl<<“Queue does not exist!”;
else if(front == 0 && rear == max – 1)
{
cout<<“\nDisplaying items:\n”;
for (i = front; i <= rear; i++)
cout<<q[i]<<” “;
cout<<endl;
}
else
{
cout<<“\nDisplaying items:\n”;
for(i=front; i!=rear; i=(i+1)%max)
cout<<q[i]<<” “;
cout<<q[rear]<<endl;
}
break;
case 4 : cout<<endl<<“Exiting program”<<endl;
exit(0);
default : cout<<endl<<“You entered an invalid choice!”;
}
cout<<endl<<“Do you wish to continue? (y/n): “;
cin>>choice;
} while (choice == ‘Y’ || choice == ‘y’);
}

/ Output */

Program Menu
1. Insert new element
2. Delete an element
3. Show list
4. Exit
Enter your choice: 1

Enter number to be inserted: 41