Queue.cpp

#include <iostream> 
#include <stdlib.h> 
using namespace std; 
class qnode  
{ 
int jobnumber; 
qnode *next; 
friend class queue; 
}; 
class queue 
{ 
qnode *front, *rear; 
public: 
void enque(int val); 
int deque(); 
int isempty(); 
void display(); 
queue() 
{ 
front = rear = NULL; 
} 
}; 
int queue::isempty() 
{ 
if (front == NULL && rear == NULL) 
return 1; 
else return 0; 
} 
void queue::enque(int val) { 
qnode *t; 
t = new qnode; 
t->jobnumber = val; 
t->next = NULL; 
// If queue is empty, then new node is front and rear both 
if (isempty())  
{ 
front = t; 
rear = t; 
}  
else  
{ // Add the new node at the end of queue and change rear 
rear->next = t; 
rear = t; 
} 
} 
int queue::deque() 
{ 
qnode *t; 
int val = -1; // Default value indica ng empty queue 
if (isempty()) { 
cout << "\nQueue is empty\n"; 
}  
else  
{ 
// Store previous front and move front one node ahead 
t = front; 
front = front->next; 
// If front becomes NULL, then change rear also as NULL 
if (front == NULL)  
{ 
rear = NULL; 
} 
val = t->jobnumber; 
delete t; 
} 
return val; // Return the job number of dequeued item (or -1 if queue is empty) 
} 
void queue::display()  
{ 
qnode *t; 
if (isempty())  
{ 
cout << "\nQueue is empty\n"; 
}  
else  
{ 
cout << "\nQueue jobnumbers: "; 
for (t = front; t != NULL; t = t->next)  
{ 
cout << "\t" << t->jobnumber; 
} 
cout << endl; 
} 
} 
int main() { 
int ch, n; 
queue obj; 
while (1)  
{ 
cout << "\n1.Add job \n2.Delete job \n3.Display job \n4.Exit"; 
cout << "\nEnter your choice: "; 
cin >> ch; 
switch (ch)  
{ 
case 1: 
cout << "\nEnter jobnumbers: "; 
cin >> n; 
obj.enque(n); 
break; 
case 2: 
if (obj.deque() == -1) 
{ 
cout << "\nNo job was deleted.\n"; 
}  
else  
{ 
cout << "\nJob deleted.\n"; 
} 
break; 
case 3: 
obj.display(); 
break; 
case 4: 
exit(0); 
default: 
cout << "\nYou entered a wrong choice.\n"; 
} 
} 
return 0; 
}