Thread: Structures - Linked List

I have 3 structures:

The first one is an array, which needs to point to class_node in order to make a list. I am not sure how to approach this. I've reviewed all the web tutorials, the book etc and running into issues trying to organize this.

Code:

struct studentReg {
       int studentID;
       char lastName[20];
       char firstName[20];
       char phoneNumber[20];
       struct classed *listPtr; //This should be a pointer to class_Node ?? yes
} structArray[NUM_STUDENTS];

typedef struct class_node {
       int studentID;
       char course[7];
       int section;
       struct class_node *next; // points to next node
} class_Node;

struct Courses {
       char course[7];
       int section;
       int creditHours;
} coursesArray[NUM_OF_COURSES];

All of the info is being pulled from text files which will be populated into the appropriate structures.

studentReg points to class_node and class_node expands depending on how many class the student is registered to. The other structure is for testing purposes to ensure the classes are accurate.

Also any tips on making this more fluent and easier to understand would be great. If the code is incorrect please feel free to yell at me and tell me what i'm doing wrong!

Ok, after trying to digest that code I'm still sorta lost, as is my partner.

Maybe we just aren't grasping some feature.

Here is the reworked code:

Code:

typedef struct class_node {
       int studentID;
       char course[7];
       int section;
       struct class_node *nextNode;
} class_Node;

class_Node classesArray[NUM_OF_CLASSES];
class_Node *nextNode = NULL;

struct studentReg {
       int studentID;
       char lastName[20];
       char firstName[20];
       char phoneNumber[20];
       class_Node *first; 
} structArray[NUM_STUDENTS];
 
struct Courses {
       char course[7];
       int section;
       int creditHours;
} coursesArray[NUM_OF_COURSES];

now, strudentReg is an array of struct's. We have 20 elements for example. Each element has a linked list of X classes all of which point to the next on in the link. (Class_node). Now, we instantiated all the info into studentReg, but not sure how to attach the struct class_node to that list properly.

once we figure that, we feel confident that we will be able to do the linked list part. from the example in the link you provided. Thanks for any help. Hope I am not frustrating anyone with my questions / lack of experience

I don't know what you think you mean by "attach the struct class_node to the list". You've embedded a list (or perhaps more properly, a pointer to the first element of your list, but that's a distinction without a difference) inside your struct.

Look at your structs... you have a lot of duplicated information between them... Why not just combine them all into a single struct and make your code a whole lot simpler?

Hints: Yes you can put arrays in structs. Yes it will be easier to sort and search. No what you have is not efficient storage.

Think about a school with 10,000 students... how you going to work that with your current setup?

We need to have an array of structures holding all the students info, and a structure linked list of the students classes he's enrolled in.

The third structure isn't mandatory, it is something we are working with for validation.

If that makes sense. This is a guideline he gave us for the project for our class.

If you have a better / more simplistic form to do what we are trying to achieve I am all ears

Ok, here's a tiny bit of code I cooked up to show just how simple random access files can be...

Code:

//random access file demo
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <string.h>

#define FNAME "random.dat"

// test data struct
struct t_Record
  { int randnum;
    char word[16]; }
  Record;



///////////////////////////////////////////////////////
// Random Access File Handlers
//

// open or create the file
FILE *FileOpen(char* Filename)
  { FILE* pFile;
    pFile = fopen(Filename,"rb+");
    if (!pFile)
      pFile = fopen(Filename,"wb+");
    return pFile; }


// Write a record to the file
int WriteRecord(FILE *File, int RecNum)
  { if( fseek(File, RecNum * sizeof(Record), SEEK_SET) == 0 )
      if ( fwrite(&Record,sizeof(Record),1,File) )
        return 1;
    return 0; }


// read a record from the file
int ReadRecord(FILE *File, int RecNum)
  { if( fseek(File, RecNum * sizeof(Record), SEEK_SET) == 0 )
      if ( fread(&Record,sizeof(Record),1,File) )
        return 1;
    return 0; }



////////////////////////////////////////////////////////
// this is for demonstration purposes only
// you would not do this in a real program
void InitFile(FILE* File)
 { int x, y;
   memset(&Record,sizeof(Record),0);
   for (x = 0; x < 1000; x++)
      { Record.randnum = rand();
        for (y = 0; y < ((Record.randnum % 15) + 1); y++)
          Record.word[y] = (rand() % 26) + 'a';
        if (! WriteRecord(File,x))
          printf("Oh drat!");  } }
 

 
//////////////////////////////////////////////////////////
// program mains
//
int main (void)
  { FILE *File;
    int Quit = 0;
    int Rec = 0; // record number

    srand(time(NULL));

    File = FileOpen(FNAME); 
    if (!File)
      { printf("Curses foiled again!\n\n");
        exit(-1); }

    // write out 1000 test records  
    printf("Create a new file? (y/n)  ");
    if ( toupper( getchar() ) == 'Y')
      InitFile(File);
  
    // lets peek
    do
      { printf("Enter a record number (0 - 999) to load : ");
        if (! scanf("%d",&Rec) )
          Quit = 1;  // enter any letter to quit
        else 
          { // read and display the record 
           if (! ReadRecord(File,Rec) ) 
              printf("Could not read record %d\n",Rec);
            else
              { printf("-----\n");
                printf("Record Number : %d\n",Rec);
                printf("Number Value  : %d\n",Record.randnum);
                printf("Record Name   : %s\n",Record.word);
                printf("-----\n"); 
                getchar();
                printf("Do you want to rename this record (y/n)? ");
                if ( toupper( getchar() ) == 'Y')
                  { printf("Enter a new name : ");
                    if ( scanf("%s",Record.word) )
                      WriteRecord(File,Rec);  } } }
      } while (! Quit); 


    fclose(File);
    return 0; }

Please note how simple the file i/o is and how easily a record can be changed and replaced in the file. Also note that only one record is ever loaded at a time... no arrays, no malloc, no complicated linked lists...

Originally Posted by quzah

Globals? Really? :eyebrow:
Quzah.

I often use a global struct with random access files... it's a lot easier than passing it around in virtually every function.

But yes... I know...

(p.s. ... Can't you find something good to say about it? )

Ahhh Pascal... those were the days!

Effing Borland just had to kill it!


I've never understood this whole "human readable" thing that seems to fire the text file fans... When's the last time a user opened a data file and looked inside? And why do they have to be able to read it even if they do?