Thread: Link List

Hi!
I have some problems with this prgram on link list.I am unable to insert and delete nodes. I also want to know how to display the items in a link list. I suspect there may be pointer problem but am unable to correct it.

I am grateful for your help.

Code:

void InsertInFront(NodePointer Head, int Num)
{
	NodePointer NewNode;
	NewNode=(NodePointer)malloc(sizeof(struct Node));
	NewNode->Data=Num;
	NewNode->Link=Head;
	Head=NewNode;
}

There is a problem with your insert function. At the end you set Head equal to the new node, but this change does not affect the Head declared in main at all.
Change the function to return a NodePointer, and do "return (NewNode);"
The call would then look like this

Head = InsertInFront(Head,number);

Code:

int DeleteFront(NodePointer Head)
{
	NodePointer Temp;
	int num;
	if(Head==NULL) {
		printf("The list is empty.Cannot delete.");
		return ;
	}

	while(Head->Link!=NULL)
	{

		Temp=Head;

		printf ( "%d\n", Temp->Data);
		Head=Head->Link;

		free(Temp);
	}
	return ;

}

This function is a bit buggy, instead of deleteing the front element, you iterate through the list freeing all the nodes, except for the last one. Try this function.

Code:

NodePointer DeleteFront(NodePointer Head)
{
	NodePointer Temp;
	int num;
	if(Head==NULL) {
		printf("The list is empty.Cannot delete.");
		return NULL; /*return the same empty list we recieved */
	}
	Temp = Head->Link; /* This will become the new head */
	free(Head); /*Free the memory */
	return Temp; /*Return the new head of the list */
}

This would also be called like this
Head = DeleteFront(Head);

hi i wesh that i have the singel code BUT sorry,,,
this is the dobuol operatios like
insert first
insert last
delete first
delete last
delete target
search
and display.
/////////////////////////////////////////////////////////////////////////////////


/////////////// DUOBLE LINK LIST OPERATIONS ///////////////////////

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
//-------------------------- >>> a structuer <<<
typedef struct
{
int id;
float gpa;
}data;
//-------------------------->>> a defanition of a duoble link list <<<
typedef struct node
{
data e;
struct node *next;
struct node *prev;
}recnode, *ptr;
//-------------------------->>> insert first in a duoble link list <<<
void ins_first(ptr *h,data newe)
{
ptr p;
p=malloc(sizeof(recnode));
p->e=newe;
p->prev=NULL;

if(*h==NULL)
{
p->next=NULL;
(*h)=p;
}
else
{
p->next=*h;
(*h)->prev=p;
(*h)=p;
}
}
//-------------------------->>> insert last in a duoble link list <<<
void ins_last(ptr *h,data newe)
{

ptr p,q;
p=malloc(sizeof(recnode));
p->e=newe;
p->next=NULL;
if((*h)==NULL)
{
(*h)=p;
(*h)->prev=NULL;
}
else
{
q=*h;
while(q->next!=NULL)
q=q->next;
q->next=p;
p->prev=q;
}
}
//-------------------------->>> new link <<<
void new_D(ptr *h)
{
*h=NULL;
}
//-------------------------->>> sertch for an element <<<
void sertch(ptr h,int t,ptr *cur)
{

*cur=NULL;

while(h!=NULL && *cur==NULL)
{
if(h->e.id==t)
*cur=h;
else h=h->next;
}
}
//-------------------------->>> delete first <<<
void del_first(ptr *h,data *z)
{
ptr p;

if(*h==NULL)printf("\nSory no list...");
else
{
if((*h)->next==NULL)
{
*z=(*h)->e;
free(*h);
}
else
{
p=*h;
*z=p->e;
(*h)=(*h)->next;
(*h)->prev=NULL;
free(p);
}
}
}
//-------------------------->>> delete last <<<
void del_last(ptr *h,data *z)
{
ptr p;

if((*h)==NULL) printf("\nSory no list...");
else
{
if((*h)->next==NULL)
{
*z=(*h)->e;
free(*h);
}
else
{
p=*h;
while(p->next!=NULL)
p=p->next;
*z=p->e;
p->prev->next=NULL;
free(p);
}
}
}
//-------------------------->>> delete target <<<
void del_target(ptr *h, int t, data *z)
{
ptr cur;
sertch(*h,t,&cur);
if(cur==NULL) printf("\nSory target not found...");
else
{
if(cur==(*h))
del_first(h,z);
else
{
if(cur->next==NULL)
del_last(h,z);
else
{
*z=cur->e;
cur->prev->next=cur->next;
cur->next->prev=cur->prev;
free(cur);
}
}
}
}
//-------------------------->>> read recored <<<
void read_rec(data *r)
{
printf("\nEnter the ID:");
scanf("%d",&r->id);
printf("\nEnter the GPA:");
scanf("%f",&r->gpa);
}
//-------------------------->>> display the link <<<
void dis(ptr h)
{
printf("\n-------------------------------");
printf("\nID GPA ");
printf("\n-------------------------------");
while(h!=NULL)
{
printf("\n%d\t\t\t%.2f",h->e.id,h->e.gpa);
h=h->next;
}
}
//////////////////////////////////////////////////////////////////////////
//>>>>>>>>>>>>>>>>>>>>>>>>>> MAIN PROGRAMM <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
//////////////////////////////////////////////////////////////////////////
main()
{
int c,t;
data r;
ptr h,cur;
new_D(&h);
do{
printf("\n\n\n\n +-------------------------------------------------+");
printf("\n |(1) insret first. |");
printf("\n | |");
printf("\n |(2) insert last. |");
printf("\n | |");
printf("\n |(3) delete first. |");
printf("\n | |");
printf("\n |(4) delete last. |");
printf("\n | |");
printf("\n |(5) delete a gevin id. |");
printf("\n | |");
printf("\n |(6) sertch for ID. |");
printf("\n | |");
printf("\n |(7) deisplay the list. |");
printf("\n | |");
printf("\n |(8) Exit. |");
printf("\n +-------------------------------------------------+");
scanf("%d",&c);



switch(c)
{

case 1:read_rec(&r);
ins_first(&h,r);system("cls");
break;
case 2:read_rec(&r);
ins_last(&h,r);system("cls");
break;
case 3:del_first(&h,&r);
break;
case 4:del_last(&h,&r);
break;
case 5:printf("\nEnter the ID:");
scanf("%d",&t);
del_target(&h,t,&r);
break;
case 6:printf("\nEnter the ID:"); scanf("%d",&t);
sertch(h,t,&cur);
if(cur==NULL)printf("\nno such ID...");
else
printf("\nID:%d\t\t\tGPA:%f",cur->e.id,cur->e.gpa);
break;
case 7:dis(h);
break;
default:printf("\nNO SUTCH CHOIS....TRY AGEN...");
}
}while(c!=8);
system("cls");

printf("\n\n\n\n\n\n\n\n\n\n THANK YOU FOR USEING MY PROGRAMM...");
}


////////////////////////////////////////////////////////////////////////////////////

i hope that you find the prolem.