Double Circular Linked List

Implementation os some some elementary operations like insert, delete, search on doubly circular linked list.

Code:

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>
#define N 100

struct dclinklist
{
	struct dclinklist *prev;  /** Stores address of previous node **/
	int roll_no;				   /** stores roll number **/
	char name[N];             /** stores Name **/
	float marks;              /** stores Marks **/
	struct dclinklist *next;  /** stores address of next node **/
};

/** Redefining dclinklist as node **/
typedef struct dclinklist node;

void init(node*);     /** Input function **/
void ins_aft(node*);  /** Function inserting before **/
node* ins_bef(node*); /** Function inserting after **/
node* del(node*);     /** Function deleting a node **/
void search(node*);   /** Function for searching node **/
void disp(node*);     /** Function for displaying node **/
void rollsrch(node*); /** Function for searching node by roll number **/
void namesrch(node*); /** Function for searching node by name **/
void marksrch(node*); /** Function for searching node by marks **/

/*** Main Function ***/
void main()
{
	node *head;
	char ch;                  /* Choice inputing varible */
	int opt;                  /* Option inputing variable*/
	static int flag=0;        /* Unchanged after iniialization */
	clrscr();
	head=(node*)malloc(sizeof(node));
	head->next=NULL; /* NULL is being over written in init function */
	head->prev=NULL;
	do
	{
again:
	printf("\nEnter your option\n");
	printf("\n1. Initialize the node\n");
	printf("\n2. Insert before a specified node\n");
	printf("\n3. Insert after a specified node\n");
	printf("\n4. Delete a particular node\n");
	printf("\n5. Search the nodes\n");
	printf("\n6. Display all the nodes\n");
	scanf("%d",&opt);
	if(flag==0 && opt!=1)
	{
		printf("\nNo. You must first initialize at least one node\n");
		goto again;
	}
	if(flag==1 && opt==1)
	{
		printf("\nInitialisation can occur only once.\n");
		printf("\nNow you can insert a node\n");
		goto again;
	}
	if(opt==4 && head->next==head)
	{
		printf("\nYou cannot delete the one and only the single node\n");
		goto again;
	}
	if(flag==0 && opt==1)
		flag=1;
	switch(opt)
	{
	case 1:
		init(head);
		break;
	case 2:
		head=ins_bef(head);
		break;
	case 3:
		ins_aft(head);
		break;
	case 4:
		head=del(head);
		break;
	case 5:
		search(head);
		break;
	case 6:
		disp(head);
		break;
	}
	printf("\nDo you wish to continue[y/n]\n");
	ch=(char)getche();
	}while(ch=='Y' || ch=='y');
	printf("\nDone by \"SHABBIR\"\n");
	printf("\nPress any key to exit\n");
	getch();
}

/*** Function for inputing data ***/
void init(node *start)
{
	start->prev=start;
	printf("\nEnter Roll number\n");
	scanf("%d",&start->roll_no);
	printf("\nEnter the name\n");
	fflush(stdin);
	gets(start->name);
	printf("\nEnter the marks\n");
	scanf("%f",&start->marks);
	start->next=start;
}

/*** Function for inserting a node after a specified node ***/
void ins_aft(node *start)
{
	int rno;                  /* Roll number for inserting a node */
	int flag=0;
	node *newnode;            /* New inputed node*/
	node *current;            /* Node for travelling the linked list*/
	newnode=(node*)malloc(sizeof(node));
	printf("\nEnter the roll number after which you want to insert a node\n");
	scanf("%d",&rno);
	init(newnode);
	current=start;
	while(current->next!=start)
	{
		/***  Insertion checking for all nodes except last  ***/
		if(current->roll_no==rno)
		{
			newnode->next=current->next;
			current->next->prev=newnode;
			current->next=newnode;
			newnode->prev=current;
			flag=1;
		}
		current=current->next;
	}
	if(flag==0 && current->next==start && current->roll_no==rno)
	{
		/***  Insertion checking for last node  ***/
		newnode->next=current->next;     /* Start is being copied */
		current->next->prev=newnode;
		current->next=newnode;
		newnode->prev=current;
		flag=1;
	}
	if(flag==0 && current->next==NULL)
		printf("\nNo match found\n");
}

/*** Function for inserting a node before a specified node ***/
node* ins_bef(node *start)
{
	int rno;                  /* Roll number for inserting a node*/
	node *newnode;            /* New inputed node */
	node *current;            /* Node for travelling the linked list*/
	newnode=(node*)malloc(sizeof(node));
	printf("\nEnter the roll number before which you want to insert a node\n");
	scanf("%d",&rno);
	init(newnode);
	current=start;
	if(current->roll_no==rno)
	{
		/*** Insertion checking for first node ***/
		newnode->next=current;
		current->prev=newnode;
		while(current->next!=start)
			current=current->next;
		newnode->prev=current;
		current->next=newnode;
		start=newnode;
		return(start);
	}
	while(current->next!=start)
	{
		/*** Insertion checking for all node except first ***/
		if(current->next->roll_no==rno)
		{
			newnode->next=current->next;
			current->next->prev=newnode;
			current->next=newnode;
			newnode->prev=current;
			return(start);
		}
		current=current->next;
	}
	/*
	If the function does not return from any return statement.
	There is no match to insert before the input  roll number.
	*/
	printf("\nMatch not found\n");
	return(start);
}

/*** Function for deleting a specified node ***/
node* del(node *start)
{
	int rno;                  /* Roll number for deleting a node*/
	node *delnode;            /* Node to be deleted */
	node *current;            /* Node for travelling the linked list*/
	printf("\nEnter the roll number whose node you want to delete\n");
	scanf("%d",&rno);
	current=start;
	if(current->roll_no==rno)
	{
		/***  Checking condition for deletion of first node  ***/
		delnode=current; /*  Unnecessary step  */
		while(current->next!=start)
			current=current->next;
		current->next=start->next;
		start->next->prev=current;
		start=start->next;
		free(delnode);
		return(start);
	}
	else
	{
		while(current->next->next!=start)
		{
			/***  Checking condition for deletion of   ***/
			/*** all nodes except first and last node  ***/
			if(current->next->roll_no==rno)
			{
				delnode=current->next;
				current->next=current->next->next;
				current->next->prev=current;
				free(delnode);
				return(start);
			}
			current=current->next;
		}
		if(current->next->next==start && current->next->roll_no==rno)
		{
			/***  Checking condition for deletion of last node  ***/
			delnode=current->next;
			free(delnode);
			current->next=start;
			return(start);
		}
	}
	printf("\nMatch not found\n");
	return(start);
}

/*** Function for searching a node ***/
void search(node *start)
{
	int ch;                   /* Choice inputing variable */
	printf("\nEnter the criteria for search\n");
	printf("\n1. Roll number\n");
	printf("\n2. Name\n");
	printf("\n3. Marks\n");
	scanf("%d",&ch);
	switch(ch)
	{
	case 1:
		rollsrch(start);
		break;
	case 2:
		namesrch(start);
		break;
	case 3:
		marksrch(start);
		break;
	default:
		rollsrch(start);
	}
}

/*** Function for searching a specified roll number ***/
void rollsrch(node *start)
{
	int rno;                  /* Roll-number to be searched */
	node *current;            /* Node for travelling the linked list*/
	printf("\nEnter the roll number to search\n");
	scanf("%d",&rno);
	current=start;
	while(current->next!=start)
	{
		if(current->roll_no==rno)
			printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
		current=current->next;
	}
	if(current->next==start && current->roll_no==rno)
		printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
}

/*** Function for searching a specified name ***/
void namesrch(node *start)
{
	char arr[20];             /* Name to be searched*/
	node *current;            /* Node for travelling the linked list*/
	printf("\nEnter the name to search\n");
	fflush(stdin);
	gets(arr);
	current=start;
	while(current->next!=start)
	{
		if(strcmp(current->name,arr)==NULL)
			printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
		current=current->next;
	}
	if(current->next==start && strcmp(current->name,arr)==NULL)
		printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
}

/*** Function for searching a specified marks ***/
void marksrch(node *start)
{
	float marks;              /* Marks to be searched */
	node *current;            /* Node for travelling the linked list*/
	printf("\nEnter the marks to search\n");
	scanf("%f",&marks);
	current=start;
	while(current->next!=start)
	{
		if(current->marks==marks)
			printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
		current=current->next;
	}
	if(current->next==start && current->marks==marks)
		printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
}

/*** Function for displaying the linked list ***/
void disp(node *start)
{
	node *current;            /* Node for travelling the linked list*/
	current=start;
	while(current->next!=start)
	{
		printf("\n %d  %s  %f",current->roll_no,current->name,current->marks);
		current=current->next;
	}
	printf("\n %d  %s  %f",current->roll_no,current->name,current->marks);
}

 

I don't see any difference but yes its a bit more explained the above one is more commented.