Double Linked List

C implementation of double linked list

Code:

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

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

/** Redefining dlinklist as node **/
typedef struct dlinklist 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 **/

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;
	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==NULL)
	{
		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=getche();
	}while(ch=='Y' || ch=='y');
	printf("\nDone by \"SHABBIR\"\n");
	printf("\nPress any key to exit\n");
	getch();
}

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

void ins_aft(node *current)
{
	int rno;             /* Roll number for inserting a node*/
	int flag=0;
	node *newnode;
	newnode=(node*)malloc(sizeof(node));
	printf("\nEnter the roll number after which you want to insert a node\n");
	scanf("%d",&rno);
	init(newnode);
	while(current->next!=NULL)
	{
		/***  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==NULL && current->roll_no==rno)
	{
		/***  Insertion checking for last nodes  ***/
		newnode->next=current->next;
		current->next=newnode;
		flag=1;
	}
	else if(flag==0 && current->next==NULL)
		printf("\nNo match found\n");
}

node* ins_bef(node *current)
{
	int rno;            /* Roll number for inserting a node*/
	node *newnode,*temp;
	newnode=(node*)malloc(sizeof(node));
	printf("\nEnter the roll number before which you want to insert a node\n");
	scanf("%d",&rno);
	init(newnode);
	if(current->roll_no==rno)
	{
		/*** Insertion checking for first node ***/
		newnode->next=current;
		current->prev=newnode;
		current=newnode;
		return(current);
	}
	temp=current;
	while(temp->next!=NULL)
	{                                       
		/*** Insertion checking for all node except first ***/
		if(temp->next->roll_no==rno)
		{
			newnode->next=temp->next;
			temp->next->prev=newnode;
			temp->next=newnode;
			newnode->prev=temp;
			return(current);
		}
		temp=temp->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(current);
}

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

void search(node *current)
{
	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(current);
		break;
	case 2:
		namesrch(current);
		break;
	case 3:
		marksrch(current);
		break;
	default:
		rollsrch(current);
	}
}

void rollsrch(node *current)
{
	int rno;
	printf("\nEnter the roll number to search\n");
	scanf("%d",&rno);
	while(current->next!=NULL)
	{
		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==NULL && current->roll_no==rno)
		printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
}

void namesrch(node *current)
{
	char arr[20];
	printf("\nEnter the name to search\n");
	fflush(stdin);
	gets(arr);
	while(current->next!=NULL)
	{
		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==NULL && strcmp(current->name,arr)==NULL)
		printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
}

void marksrch(node *current)
{
	float marks;
	printf("\nEnter the marks to search\n");
	scanf("%f",&marks);
	while(current->next!=NULL)
	{
		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==NULL && current->marks==marks)
		printf("\n%d\t%s\t%f\n",current->roll_no,current->name,current->marks);
}

void disp(node *current)
{
	while(current!=NULL)
	{
		printf("\n%d\t%s\t%f",current->roll_no,current->name,current->marks);
		current=current->next;
	}
}