Question

In this program, I want to put the element in the list rather than an array. And lastly print out the list.

eg.
simon 22
suzie 24
…

However, I dont really understand how to manipulate the list, and how I can build the heap and retrieve it. I did some research about how to do it. And this is what I come up.
And some of the error comes out and I have no idea how to fix.

error: 'ptr' undeclared (first use in this function)
arrays.c:37:5: note: each undeclared identifier is reported only once for each function     it appears in
arrays.c: In function 'main':
arrays.c:62:9: error: expected identifier or '(' before '=' token
arrays.c:69:5: warning: passing argument 1 of 'insert' from incompatible pointer type
arrays.c:28:13: note: expected 'struct Record *' but argument is of type 'struct Record **'

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


/* these arrays are just used to give the parameters to 'insert',
   to create the 'people' array */
char *names[7]= {"Simon", "Suzie", "Alfred", "Chip", "John", "Tim",
          "Harriet"};
int ages[7]= {22, 24, 106, 6, 18, 32, 24};


/* declare your struct for a person here */
/* */
typedef struct Record{
    char *names;
    int ages;
    struct Record *next;
}  Record;

char getname(Record *names){
    return names;
}

int getage(Record *ages){
    return ages;  
}

static void insert (Record *p, char *s, int n) {

//p[(*)] = malloc(sizeof(person));

/*static int nextfreeplace = 0;*/
    Record *headptr = NULL;

    while(!reached_eof(p)){

/* allocate heap space for a record */
        ptr =(Record*) malloc(sizeof(Record));

        if(ptr == NULL){  
            abort();
            printf("memory allocation fail"); 
            exit(1);  
        }
        else{
            printf("memory allocation to person  - %s - \n", s);      
        }

        ptr->name = getname(p);
        ptr->age = getage(p);

        /* link new object into the list */
        ptr->next = headptr;
        headptr = ptr;

    }
}       


int main( int argc, char **argv) {

    /* declare nextinsert */
    int  = 0;            

    /* declare the people array here */
    Record *p, *headptr;
    headptr = NULL;

    //insert the members and age into the unusage array. 
    for ( int i=0 ; i < 7; i++) {
        insert (p, names[i], ages[i]);

        /* do not dereference the pointer */
    }

    /* print out a line before printing the names and ages */
     printf("\n");


    /* print the people array here*/
    for (int i=0; i < 7; i++) {
        printf("The name is: %s, the age is:%i\n", p[i]->names, p[i]->ages);
    }


    /* This is the third loop for call free to release the memory allocated by malloc */
    /* the free()function deallocate the space pointed by ptr. */
    for(int i=0; i<7;i++){
        free(p[i]);
    }
}

Answer 1

First of all

The following code is wierd

char getname(Record *names){
  return names;
}

int getage(Record *ages){
  return ages;  
}

I do not see any real need for the above function.

even these lines

ptr->name=getname(p);
ptr->age=getage(p);

you can relace them with

ptr->name=s;
ptr->age=n;

The following function contains many errors and strange codes:

static void insert (Record *p, char *s, int n) {

//p[(*)] = malloc(sizeof(person));

/*static int nextfreeplace = 0;*/
   Record *headptr = NULL;

   while(!reached_eof(p)){
/* allocate heap space for a record */
ptr =(Record*) malloc(sizeof(Record));

if(ptr == NULL){  
   abort();
   printf("memory allocation fail"); 
   exit(1);  
}else{
   printf("memory allocation to person  - %s - \n", s);      
}

Why you are using while loop. and you missed the definition of ptr pointer and you have note communicate the neaw header at the end of the function. here after how you can fix it:

static void insert (Record **header, char *s, int n) {

   Record *ptr;
   ptr =(Record*) malloc(sizeof(Record));

    if(ptr == NULL){  
       abort();
       printf("memory allocation fail"); 
       exit(1);  
    }else{
       printf("memory allocation to person  - %s - \n", s);      
    }
    ptr->name=s;
    ptr->age=n;

    /* link new object into the list */
    ptr->next=*header;
    *headptr=ptr;
}

And in your main function:

int main(int argc, char **argv) {


   int  i= 0;
  Record *p, *headptr=NULL;

for (int i=0; i < 7; i++) {
insert (&headptr, names[i], ages[i]);
/* do not dereference the pointer */
  }

 for (int i=0; i < 7; i++) { /* this will print from array*/
    printf("From array  The name is: %s, the age is:%i\n", p[i]->names, p[i]->ages);
}

for (p=headptr; p!=NULL; p=p->next) {  /* this will print from linked list*/
    printf("From linked list The name is: %s, the age is:%i\n", p->names, p->ages);
}


}