Queue

Queue is a FIFO structure. FIFO means first in first out. For queue, there is a front and a back just like linked list has head and tail. Its just like a physical queue, one ends through the back and leaves from the front. Without much ado, Here is a C program for queue:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE  100
int count=0;
typedef struct node{
 int value;
 struct queue *next;
 struct queue *prev;
}queue;

queue *front=NULL;
queue *back=NULL;

queue *createnode(int a)
{
 queue *newstack;
 newstack=(queue*)calloc(1,sizeof(queue));
 newstack->value=a;
 newstack->prev=NULL;
 newstack->next=NULL;
 return newstack;
}

int isempty()
   {
       if(count==0)
       {return 1;}
       else
       {return 0;}
    }

int isfull()
    {
     if(count==SIZE)
     {return 1;}
     else
     {return 0;}
    }

void enqueue(int a)
{   if(isfull()==1)
   {
    printf("overflow condition: queue full");
   }
 else
   {count+=1;
 queue *newqueue = createnode(a);
 if(back==NULL)
 {
 back=newqueue;
 front=back;
 }
 else
 {
  back->next=newqueue;
  newqueue->prev=back;
  back=newqueue;
 }
   }
}
char peek()
{
    return back->value;
}
char dequeue()
    {   if(isempty()==1)
        {
         printf("underflow condition:empty queue");
        }
        else
        {if(count==1)
        {   int c;
         c=back->value;
         back=NULL;
         front=NULL;
         count=count-1;
         return c;
        }
        else
     {int c;
     c=front->value;
  front=front->next;
  front->prev=NULL;
  count=count-1;
  return c;

     }
       }
    }
void printqueue(queue *n)
{
        while(n!=NULL)
        {
                printf("%d->",n->value);
                n=n->next;
        }
        printf("NULL");
}

int main(void) {
    queue good_boy;
    int i;
    for(i=1;i<5;i++)
    {
        enqueue(i);
    }
    printqueue(front);
        return 0;
}