Deletion in linked list..

[Vish0203]

Hi everyone,
I'm facing problem in deleting a node in del() used in my program.
Suppose, i've added a city as Delhi, and at the time of deleting, i type the name as delhi, the compiler gives a processor fault. But, i want it to display the line number 95.
I found out that there is error in while part in line number 85, but i dont know how to overcome that problem.

Anyone there to help me out with this????????????????????????

NOTE: I dont want to use any extra integer to detect the position.

My program:

#include<conio.h>
#include<stdio.h>
#include<string.h>
#include<alloc.h>
struct city
 {
  char c[30];
  struct city *next;
 }*head=NULL,*tail=NULL;
void add();
void del();
void ins();
void disp();
void main()
{
 int n;
 while(1)
 {
 XY:
 printf("\n\nLIST OF CITIES\n^^^^^^^^^^^^^^");
 printf("\n1. Add a city.");
 printf("\n2. Delete a city.");
 printf("\n3. Insert a city.");
 printf("\n4. Display.");
 printf("\nEnter your choice.. ");
 scanf("%d",&n);
 switch(n)
  {
    case 1: add(); break;
    case 2: del(); break;
    case 3: ins(); break;
    case 4: disp(); break;
    default: printf("See the options BHOSDI KE");
                printf("\npress enter to re-enter");
                if(getch()=='\r')
                 {
                  clrscr();
                  goto XY;
                 }
  }
 printf("Do you want to continue?? (Y/N) ");
 if(getche()=='y'||getche()=='Y')
  continue;
 else if(getche()=='n'||getche()=='N')
  break;
 }
}
 void add()
  {
    char name[30];
    printf("Enter the name of city: ");
    scanf("%s",name);
    struct city *curr;
    curr=(struct city *)malloc(sizeof(struct city));
    strcpy(curr->c,name);
    if(head==NULL)
     {
        head=curr;
        tail=curr;
        tail->next=NULL;
     }
    else
     {
      tail->next=curr;
      tail=curr;
      tail->next=NULL;
     }
  }

 void del()
  {
    XY:
    char del_c[30];
    printf("Enter the name of city to be deleted: ");
    scanf("%s",del_c);
    struct city *tmp,*prev;
    tmp=head;
    if(strcmp(del_c,head->c)==0)
     {
      head=head->next;
      free(head);
     }
    else
    {
     while(strcmp(del_c,tmp->c)!=0)
      {
        prev=tmp;
        tmp=tmp->next;
      }
     prev->next=tmp->next;
     free(tmp);
    }
    if(strcmp(del_c,head->c)!=0||strcmp(del_c,tmp->c)!=0)
     {
      printf("City is not there in list");
      goto XY;
     }
  }

 void ins()
  {
    char ins_c[30]; int pos,m=1;
    printf("Enter the position where you want to insert= ");
    scanf("%d",&pos);
    printf("Enter the city to be inserted: ");
    scanf("%s",ins_c);
    struct city *tmp,*curr;
    curr=(struct city *)malloc(sizeof(struct city));
    tmp=head;
    strcpy(curr->c,ins_c);
    while(m<pos-1)
     {
      tmp=tmp->next;
     }
    curr->next=tmp->next;
    tmp->next=curr;
  }

 void disp()
  {
    struct city *ptr;
    for(ptr=head;ptr!=NULL;ptr=ptr->next)
     {
      printf("\n\n%s",ptr->c);
     }
    printf("\n\n");
  }

[TrustyTony]

Equalize the case of compared strings http://www.codingunit.com/c-reference-ctype-h-convert-to-lower-case-tolower

[TrustyTony]

You should use stdlib.h not alloc.h and system("CLS") instead of nonstandard clrscr.
main should return int

[Vish0203]

system("CLS")

the compiler says
"undefined symbol_system in module"

[TrustyTony]

http://www.thinkage.ca/english/gcos/expl/c/lib/system.html

[Sokurenko]

please comment your code next time, or explain it to your cat hope this helps :)

void del()
{
   XY:
   char del_c[30];
   printf("Enter the name of city to be deleted: ");
   scanf("%s",del_c);
   struct city *tmp,*prev;
   tmp = head;
   if(strcmp(del_c, head->c) == 0)//if data that head points to matches or just segfault if null pointer
   {
      head = head->next;//make head point to next element
      free(head);//delete next element
   }
   else
   {
      while(strcmp(del_c,tmp->c) != 0)//while does not match // better to look for NULL pointer before accessing
      {
         prev = tmp;
         tmp = tmp->next;//search from head till the system error or we find something before
      }
      prev->next = tmp->next;//we found something or not, lets make something point somewhere after next in linked list
      free(tmp);//free something maybe would be ok if we find something
   }
   if(strcmp(del_c,head->c) != 0 || strcmp(del_c,tmp->c) != 0)//head might not exist - seg fault or tmp
   {
      printf("City is not there in list");
      goto XY;//using goto is bad practise
   }
}

[Vish0203]

please comment your code next time, or explain it to your cat hope this helps :)

I've mentioned the line numbers where i'm facing probs..!!!

@pyTony

Actually i use Borland turbo c++ 4.5, and it gives that error.. is it cuz of different versionof C????????

[Vish0203]

@sokurenko

yea i agree with you.. Using goto is bad but its just a small program, so i dont think it'll be much complecated by that!

[Sokurenko]

I've mentioned the line numbers where i'm facing probs..!!!

    if(head != NULL)//check does head point somewhere on initialised memmory cause after free it should point to NULL
    {
        if(strcmp(del_c,head->c) != 0)//does it have data that we need
        {
           //handle
        }
    }