Queue Program In C

We shall see the queue implementation in C programming language here. To learn the theory aspect of queue, click on visit previous page.

Queue Implementation in C

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX 6

int intArray[MAX];
int front = 0;
int rear = -1;
int itemCount = 0;

int peek() {
   return intArray[front];
}

bool isEmpty() {
   return itemCount == 0;
}

bool isFull() {
   return itemCount == MAX;
}

int size() {
   return itemCount;
}  

void insert(int data) {

   if(!isFull()) {
	
      if(rear == MAX-1) {
         rear = -1;            
      }       

      intArray[++rear] = data;
      itemCount++;
   }
}

int removeData() {
   int data = intArray[front++];
	
   if(front == MAX) {
      front = 0;
   }
	
   itemCount--;
   return data;  
}

int main() {
   /* insert 5 items */
   insert(3);
   insert(5);
   insert(9);
   insert(1);
   insert(12);

   // front : 0
   // rear  : 4
   // ------------------
   // index : 0 1 2 3 4 
   // ------------------
   // queue : 3 5 9 1 12
   insert(15);

   // front : 0
   // rear  : 5
   // ---------------------
   // index : 0 1 2 3 4  5 
   // ---------------------
   // queue : 3 5 9 1 12 15
	
   if(isFull()) {
      printf("Queue is full!
");   
   }

   // remove one item 
   int num = removeData();
	
   printf("Element removed: %d
",num);
   // front : 1
   // rear  : 5
   // -------------------
   // index : 1 2 3 4  5
   // -------------------
   // queue : 5 9 1 12 15

   // insert more items
   insert(16);

   // front : 1
   // rear  : -1
   // ----------------------
   // index : 0  1 2 3 4  5
   // ----------------------
   // queue : 16 5 9 1 12 15

   // As queue is full, elements will not be inserted. 
   insert(17);
   insert(18);

   // ----------------------
   // index : 0  1 2 3 4  5
   // ----------------------
   // queue : 16 5 9 1 12 15
   printf("Element at front: %d
",peek());

   printf("----------------------
");
   printf("index : 5 4 3 2  1  0
");
   printf("----------------------
");
   printf("Queue:  ");
	
   while(!isEmpty()) {
      int n = removeData();           
      printf("%d ",n);
   }   
}

Output

If we compile and run the above program, it will produce the following result −

Queue is full!
Element removed: 3
Element at front: 5
----------------------
index : 5 4 3 2 1 0
----------------------
Queue: 5 9 1 12 15 16