Thread: ordered linked list

Typically, you'd want to find the correct location of the node you're trying to insert, then insert it.

Yes that is what I'm trying to do. So I need to make sure that the data is also in alphabetic order. So i enter in the data it looks at whats there and then prints it to the file in the order. Or is there a differnt way that i should be doing in. I have changed my insert funcation to this. I added the void.

Code:

void InsertNode (PERSON *Top, PERSON *Node )
{
PERSON *Here, /* Node being compared to new node */  
*Prev; /* Node in front of Here node */
if (Top == NULL)/* List is empty – Place new node at top of list */
Top = Node;
else { /* Top != NULL *//* Start at Top of list */
Here = Top;
if (Here->LName > Node->LName) {               
Node->Next = Top;
Top = Node;
}
else {/* Search for place to insert new node */
Prev = Top;
Here = Prev->Next;
while ( (Here != NULL) &&
(Here->LName < Node->LName) ) {
Prev = Here;
Here = Here->Next;
}/* Insert into list at found spot */
Node->Next = Prev->Next;
Prev->Next = Node;
}
} /* end of Top != NULL */
}

I'm calling it by

Code:

  InsertNode (Top, Node);  //read insernode function

I still do not thin that Im calling in the funcation. Or if Im calling it at the wrong place of my program.

ok so im not passign the data. I htough that I could use this to pass the data. But am having trouble definging it any help please.

Code:

    	for(i = 0; i< count ;i++)
	{
		STU->LName = (struct person_t  *) malloc(sizeof(person_t));
		if(!LName)
			return -1;
		LName->LName= Top ;
		InsertNode(LName, &Top, &Node);
		i++;
	}

here are my errors
130 E:\lab4.cpp incompatible types in assignment of `person_t*' to `char[26]'
131 E:\lab4.cpp `LName' undeclared (first use this function)
(Each undeclared identifier is reported only once for each function it appears in.)
132 E:\lab4.cpp return-statement with a value, in function returning 'void'

Code:

STU->LName = (struct person_t  *) malloc(sizeof(person_t));
		if(!LName)
			return -1;
		LName->LName= Top ;
		InsertNode(LName, &Top, &Node);
		i++;

You already declared this as an array in your struct. So space was already allocated to it when you declared LName. All you need to do is fill that array up.

132 E:\lab4.cpp return-statement with a value, in function returning 'void'

This error is pretty much self-explanitory. You have a function declared as void. You're returning something which is not void...

Code:

Here->LName > Node->LName

Again, here you're comparing pointers, not strings. I've told you this before. Use strcmp() !

The logic behind your insertion seems fine. Your understanding of C, not so fine.
Anyhow, that should get you a little further.

Yes, otherwise you're comparing addresses.

Here's how strcmp works. You call strcmp(s1,s2). The function will return 0 if both string are equal (AKA s1 = "abc" and s2 = "abc")
It will return smaller than zero if s1 is lexicographically inferior to s2 (s1 = "abc", s2 = "bc")
It will return greater than zero if s1 is lexicographically superior to s2 (s1 = "bc", s2 = "abc").

Oh, and strcmp is in <string.h>, so make sure to include the header.

so instead of if i would do

Code:

strcmp(Here->LName ,Node->LName)

thatis here my if sttement was. thisis how ichanged it in the code. I still do nto see it going into the funcation. am i wrong fro putting the Insertfuncation into the void amend_file( char file[], PERSON *STU ); and void show_file I should have it in the case can add it then a statment to print to the screen or an i all the way off.

Code:

 #include <assert.h>.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define Nlen    26

typedef struct person_t {
   char FName[Nlen];
   char LName[Nlen];
   char Sex;
   char Grade;
   struct person_t *Next;
  } PERSON;

struct person_t  *Top = NULL;         
struct person_t  *Node = NULL;


/*********************************************************************
 Funstion to Ordered linked list
 This is where i will call the Last name and put it into the linked   
 list ordered by last name. 
 
********************************************************************/
PERSON* InsertNode (PERSON *Top, PERSON *Node )
{
PERSON *Here, /* Node being compared to new node */  
*Prev; /* Node in front of Here node */

    if (Top == NULL)/* List is empty – Place new node at top of list */
      Top = Node;
         else { /* Top != NULL *//* Start at Top of list */
          Here = Top;
          
    strcmp (Here->LName , Node->LName);             
     Node->Next = Top;
     Top = Node;
    
          // else {/* Search for place to insert new node */
            // Prev = Top;
             //Here = Prev->Next;
 
   while ( (Here != NULL) &&(Here->LName < Node->LName) ) {
       Prev = Here;
       Here = Here->Next;
        }/* Insert into list at found spot */
        
Node->Next = Prev->Next;
Prev->Next = Node;
} /* end of Top != NULL */
return Top;
}
/*************************************************************
end of  Funstion to Ordered linked list
***************************************************************/

void amend_file( char file[], PERSON *STU ); 
void show_file( char file[], PERSON *STU );


int main (void)
{
   PERSON *STU;
   int Ans;
        char file[] = "e:\\data.txt";
    int Records [100];
     FILE *fin = fopen(file, "a+");
     struct person_t  *Top = NULL;    
	struct person_t  *Node = NULL;
	
    
    
  do
   {
      printf("\n\n"
             "1. Enter new record\n"
             "2. Display List\n"
             "3. Quit\n\n");
      printf("Prompt: ");
      fflush(stdout);
      if ( scanf("%d", &Ans) == 1 ) /* get answer */
      {
        fgets(STU->FName,sizeof(STU->FName),stdin);
         if (STU == NULL)
         {
            perror("PERSON");
            exit(EXIT_FAILURE);
         }
         switch(Ans)
         {
            case 1:
               amend_file(file, STU);  //calls the amend file funcation 
              break;
            case 2:
               show_file(file, STU);  //calls teh show file funcation
               break;
            case 3: default:
               Ans = 3;
               break;
         }
      } /* /get answer */
   }
    while ( Ans != 3 );
    
      fflush(stdout);
      free(STU);
      getchar ();
   return EXIT_SUCCESS;
}

/*************************************************************************
* amend_file: Enter stuff into the working file.
*
**************************************************************************/
void amend_file( char file[], PERSON *STU )
{
     int i, count;
   assert(STU != NULL);
   FILE *fin = fopen(file, "a+");
   if ( fin == NULL )
   {
      perror(file);
      exit(EXIT_FAILURE);
   }
   printf("Enter new record: ");
   printf ("\nEnter students First name ( up to %d letters):", Nlen);
   printf ("\nEnter students  Last name  ( up to %d letters):", Nlen);
   printf ("\nPlease enter Sex");
   printf ("\nPlease enter Grade\n");
   scanf("%s %s %c %c", STU->FName, STU->LName, &STU->Sex,
      &STU->Grade);
      InsertNode (Top, Node);
        fprintf(fin, "%s %s %c %c\n", STU->LName, STU->FName, STU->Sex, STU->Grade);
           fflush(fin);
            fclose(fin); 
      }


/******************************************************************************
* show_file: Reads the working file.
* Bare bones again...
******************************************************************************/
void show_file ( char file[], PERSON *STU )
{
  assert(STU != NULL);
  int b = 1;
  FILE *fin = fopen(file, "rb");
    
  if (file == NULL)
  {
    perror(file);
    exit(EXIT_FAILURE);
  }
  while (fscanf(fin, "%s %s %c %c", STU->FName, STU->LName, &STU->Sex,
     &STU->Grade)== 4)
  {   
   InsertNode (Top, Node);  //read insernode function
    b++;          
    printf("Record %d: %s %s %c %c\n", b, STU->FName, STU->LName,
       STU->Sex, STU->Grade);
  }
  fclose(fin);
}

ugh.

Code:

if(strcmp(s1,s2) < 0)
{
    //  s1 goes before s2
}
else
{
    // s1 goes after s2
}