cq.c

#include <stdio.h>

#define MAX 10
int queue[MAX];
int front=-1, rear=-1;
void insert(void);
int delete_element(void);
int peek(void);
void display(void);
int main()
{
int option, val;

do
{
		
printf("\n ***** MAIN MENU *****");
		
printf("\n 1. Insert an element");
		
printf("\n 2. Delete an element");
		
printf("\n 3. Peek");
		
printf("\n 4. Display the queue");
		
printf("\n 5. EXIT");
		
printf("\n Enter your option : ");
		scanf("%d", &option);
		
switch(option)
		{
			case 1:
				
insert();
				
break;
			case 2:
				
val = delete_element();
				
if(val!=-1)
				
printf("\n The number deleted is : %d", val);
				
break;
			case 3:
				
val = peek();
				
if(val!=-1)
				
printf("\n The first value in queue is : %d", val);
				
break;
			case 4:
				
display();
				
break;
		}
}while(option!=5);

return 0;
}
void insert()
{
int num;
printf("\n Enter the number to be inserted in the queue : ");
scanf("%d", &num);
if(front==0 && rear==MAX-1)
		printf("\n OVERFLOW");
else if(front==-1 && rear==-1)
{
		
front=rear=0;
		queue[rear]=num;
}
else if(rear==MAX-1 && front!=0)
{
		
rear=0;
		queue[rear]=num;
}
else
{
		rear++;
		queue[rear]=num;
}
}
int delete_element()
{
int val;
if(front==-1 && rear==-1)
{
		printf("\n UNDERFLOW");
		return -1;
}
val = queue[front];
if(front==rear)
		front=rear=-1;
else
{
		if(front==MAX-1)
			
front=0;
		else
			front++;
}
return val;
}
int peek()
{
if(front==-1 && rear==-1)
{
		
printf("\n QUEUE IS EMPTY");
		return -1;
}
else
{
		return queue[front];
}
}
void display()
{
int i;
printf("\n");
if (front ==-1 && rear==-1)
		
printf ("\n QUEUE IS EMPTY");
else
{
		if(front<rear)
		{
			for(i=front;i<=rear;i++)
				
printf("\t %d", queue[i]);
		}
		else
		{
			for(i=front;i<MAX;i++)
				
printf("\t %d", queue[i]);
			
for(i=0;i<=rear;i++)
				
printf("\t %d", queue[i]);
		}
}
}