3.4 Programming Projects

#include<iostream>
 using namespace std;
 const int maxqueue=10;
 typedef int queue_entry;
 enum Error_code{success,overflow,underflow};
 class queue
 {
 public:
  queue(void);
  Error_code serve();
  Error_code append(const queue_entry &item);
  Error_code retrieve(queue_entry &item)const;
  int size()const;
  void clear();

 

protected:
  int count;
  int front,rear;
  queue_entry entry[maxqueue];

};

 

queue::queue(void)
 {
  count = 0;
  rear = maxqueue-1;
  front=0;
 }

 Error_code queue::append(const queue_entry &item){
   if(count>=maxqueue)
    return overflow;
   count++;
   rear=((rear+1)==maxqueue)?0:(rear+1);
   entry[rear]=item;
   return success;}

 Error_code queue::serve(){
   if(count<=0)
    return underflow;
   count--;
   front=((front+1)==maxqueue)?0:(front+1);
   return success;}

 Error_code queue::retrieve(queue_entry &item)const{
   if(count<=0)
    return underflow;
   item=entry[front];
   return success;}

 int queue::size()const{
  return count;}

 void  queue::clear(){
     count=0;
     rear=front;
 }

 void help();
 void introduction();
 char get_command();
 bool do_command(char c,queue &test_queue);
 int main(){
  queue test_queue;
  introduction();
  while(do_command(get_command(),test_queue));}

 void help(){
   cout<<endl
   <<"This program allows the user to enter one command"<<endl
   <<"(but only one)on each input line."<<endl                                             
   <<"For example,if the command S is entered,then"<<endl
   <<"the program will serve the front of the queue"<<endl
   <<endl
   <<"The valid commands are:"<<endl
   <<"A - Append the next input character to the extended queue"<<endl
   <<"S - Serve the front of the extended queue"<<endl
   <<"R - Retrieve and print the front entry"<<endl
   <<"# - The current size of the extended queue"<<endl
   <<"C - Clear the extended queue (same as delete)"<<endl
   <<"P - Print the extended queue"<<endl
   <<"H - This help screen"<<endl
   <<"Q - Quit"<<endl
   <<"Press <Enter> to continue"<<flush;
  char c;
  do{
   cin.get(c);
  }while (c!='\n');}

 void introduction(){
  cout<<"press <H> for help"<<endl;

}

char get_command(){
  char c;
  cout<<"select command and press <enter>";
  cin>>c;
  if(c=='A'||c=='S'||c=='R'||c=='#'||c=='C'||c=='P'||c=='H'||c=='Q')
   return c;
  else
   cout<<"please enter a valid command or <H> for help"<<endl;
 }

bool do_command(char c,queue &test_queue){
  bool continue_input=true;
  queue_entry x;
  switch(c){
  case'A':
   cout<<"enter new data to insert";
   cin>>x;
   if(test_queue.append(x)==overflow)
    cout<<"queue is full"<<endl;
   break;

 case'S':
   if(test_queue.serve()==underflow)
    cout<<"queue is empty"<<endl;
   break;

 case'R':
   if(test_queue.retrieve(x)==underflow)
    cout<<"queue is empty"<<endl;
   else
    cout<<endl
    <<"the first entry is:"<<x
    <<endl;
   break;

 case'#':
   test_queue.size();
   break;

 case'C':
   test_queue.clear();
   break;

 case'P':

  break;

 case'H':
   help();
   break;

 case'Q':
   cout<<"extended queue demonstration finished."<<endl;
   continue_input=false;
   break;
  }
  return continue_input;
 }