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I am trying to implement polynomials using linked lists and circular representation i.e. link of the last node pointing to the first node(header). When I create my first polynomial using the function create all the links get established perfectly, including the last, circular one. However the moment I create a second polynomial using the same function 'create',the circular link of the first polynomial breaks off. (All the other links of the first polynomial remain intact). I'm using the turboC++ compiler (I've saved my file with a .c extension.)

The create function is as follows:

void create(poly header)
{
    poly temp;
    int i,n;
    temp=header;
    printf("\nEnter the number of terms: "); scanf("%d",&n);
    if(n==0)
    {
        header->link=header;
        return;
    }
    printf("\nEnter the coefficients and exponents:\n");
    for(i=0;i<n;i++)
    {
        temp->link=malloc(sizeof(poly));
        temp=temp->link;
        printf("\nCoef: "); scanf("%d",&temp->coef);
        printf("Exp : "); scanf("%d",&temp->exp);
        if(i==n-1)
            temp->link=header;
    }
}

The main function is as follows:

void main()
{
    clrscr();
    header1=malloc(sizeof(poly));
    header2=malloc(sizeof(poly));
    printf("Polynomial 1:\n");
    create(header1);
    printf("\nPolynomial 2:\n");
    create(header2);
    printf("\n\nP1: ");
    display(header1);
    printf("\n\nP2: ");
    display(header2);
    getch();
}

The display function is as follows:

void display(poly header)
{
    poly temp;
    if(header->link==header)
        printf("Zero polynomial\n");
    temp=header->link;
    while(temp!=header)
    {
        if(temp->exp==header->link->exp||temp->coef<0)
            printf("%d(x^%d)",temp->coef,temp->exp);
        else
            printf(" + %d(x^%d)",temp->coef,temp->exp);
        temp=temp->link;
    }
}

Both the functions create and display work perfectly; I've checked by creating a single polynomial and printing it.

I have traced the program and checked for the links (I've used the polynomials 3x^2+2x+1 and 2x^2+1 as my first and second polynomials respectively).

This is how I've done the declarations:

struct POLY
{
    int coef,exp;
    struct POLY *link;
};

typedef struct POLY* poly;

poly header1=NULL,header2=NULL,header3=NULL; //global

My problem may sound trivial but please help me. I'm a novice to using linked lists.

Arjun Desai
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  • Looks more like C to me, and you're compiling it as C, so I've updated your tags. – Thomas Oct 22 '14 at 13:30
  • Looks like it works when compiled with GCC-4.9.1. I did have to invent the poly struct based on how it seems to be used and create dummies for `clrscr()` and `getch()` – r_ahlskog Oct 22 '14 at 13:51
  • It would help to have the declaration of the `poly` typedef, and also of the global `header1` and `header2` variables. – John Bollinger Oct 22 '14 at 15:07
  • In any case, I can't see how this is supposed to work. If `poly` is a pointer type then your `malloc()`s are likely allocating the wrong amount of memory. If it is *not* a pointer type (but `header1` and `header2` are pointers to its type) then the calls to `create()` and `display()` pass arguments of the wrong type. – John Bollinger Oct 22 '14 at 15:12
  • Use this style to avoid calling `malloc()` with incorrect size: `header1 = malloc(sizeof *header1);` or `pointer = malloc(n * sizeof *pointer)`. – chux - Reinstate Monica Oct 22 '14 at 18:06
  • Hey dear John Bollinger THANKS THANKS THANKS THANKS :) :) a lot for answering my question. It helped a lot...in fact it just helped. Yes, u r right i was allocating the wrong amount of memory. I just replaced 'poly' with 'struct POLY' in malloc()'s and got the desired output. I can't tell u how much ur answer means to me. Once again loads of thanks :) – Arjun Desai Oct 22 '14 at 21:21

1 Answers1

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If poly is a pointer type then your malloc()s are likely allocating the wrong amount of memory. – John Bollinger

I just replaced 'poly' with 'struct POLY' in malloc()'s and got the desired output. – Arjun Desai

Armali
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