Creating a polynomial with a linked list in C

Question

I am creating a polynomial using a linked list in C, and I'm having a problem. Can someone please help me with my code? In the create function, I have just created a node, and I want to place the node in the right position in the function insert, and I then want the polynomial p1 to be returned.

I am also not able to understand how the return statement is going to work. Please tell me what the errors in the code are with my approach.

struct node
{
    int cof;
    int exp;
    struct node *link;
};
struct node * create(struct node *q)
 {
  int i,n;
  printf("enter the number of nodes");
  scanf("%d",&n);
  struct node *ptr=(struct node *)malloc (sizeof(struct node));
  for(i=0;i<n;i++)
  {
                  printf("entre the coefficient and exponent respectivly");
                  scanf("%d%d",&ptr->cof,&ptr->exp);
                  ptr->link=NULL;
                  q=insert(ptr,q);
  }
  return q;
 }
struct node * insert(struct node *ptr,struct node *p)
 {
  struct node *temp,*b;
  if(p==NULL)
  p=ptr;
  else
  {
      if((p->exp)<(ptr->exp))
      {
                              ptr->link=p;
                              p=ptr;
      }
      else
      {
          temp=p;
          while((temp!=NULL)||((temp->link->exp)<(ptr->exp)))
          temp=temp->link;
          b=temp->link;
          temp->link=ptr;
          ptr->link=b;
      }
  }
  return p;
  }
void display(struct node *ptr)
 {
   struct node *temp;
  temp=ptr;
  while(temp!=NULL)
  {
                   printf("%d x ^ %d + ",temp->cof,temp->exp);
                   temp=temp->link;
  }
 }

 int main()
  {
  printf("enter the first polynomial");
  struct node *p1=NULL,*p2=NULL; 
  p1=(struct node *)malloc(sizeof(struct node));
  p2=(struct node *)malloc(sizeof(struct node));

  p1=create(p1);

  printf("entr secon dpolynimial");
  create(p2);

  display(p1);
  display(p2);

  getch();
  return 0;
 }

Question1: how many nodes do you want to insert? Question2: how many do you allocate ? — wildplasser, Nov 16 '13 at 16:20

score 1 · Answer 1 · answered Nov 16 '13 at 23:26

This code works for at least some inputs:

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

struct node
{
    int cof;
    int exp;
    struct node *link;
};

struct node *create(struct node *q);
struct node *insert(struct node *ptr, struct node *p);
void display(char const *tag, struct node *ptr);
void err_exit(char const *tag);

struct node *create(struct node *q)
{
    int i, n;
    printf("enter the number of nodes: ");
    if (scanf("%d", &n) != 1)
        err_exit("Read error (number of nodes)");
    for (i = 0; i < n; i++)
    {
        struct node *ptr = (struct node *)malloc(sizeof(struct node));
        if (ptr == 0)
            err_exit("Out of memory (1)");
        printf("enter the coefficient and exponent respectively: ");
        if (scanf("%d%d", &ptr->cof, &ptr->exp) != 2)
            err_exit("Read error (coefficient and exponent)");
        ptr->link = NULL;
        q = insert(ptr, q);
        display("after input", q);
    }
    return q;
}

struct node *insert(struct node *ptr, struct node *p)
{
    struct node *temp, *b;
    if (p == NULL)
        p = ptr;
    else
    {
        display("insert: p   = ", p);
        display("insert: ptr = ", ptr);
        if (p->exp < ptr->exp)
        {
            ptr->link = p;
            p = ptr;
        }
        else
        {
            temp = p;
            while ((temp->link != NULL) && (temp->link->exp < ptr->exp))
                display("insert: tmp = ", temp),
                temp = temp->link;
            display("insert: post loop", temp);
            b = temp->link;
            temp->link = ptr;
            ptr->link = b;
        }
    }
    return p;
}

void display(char const *tag, struct node *ptr)
{
    struct node *temp;
    const char *pad = "";
    temp = ptr;
    printf("%s: ", tag);
    while (temp != NULL)
    {
        printf("%s%d x ^ %d", pad, temp->cof, temp->exp);
        temp = temp->link;
        pad = " + ";
    }
    putchar('\n');
}

int main(void)
{
    printf("enter the first polynomial:\n");
    struct node *p1 = NULL, *p2 = NULL;

    p1 = create(p1);

    printf("enter the second polynomial:\n");
    p2 = create(p2);

    display("p1", p1);
    display("p2", p2);

    return 0;
}

void err_exit(char const *tag)
{
    fprintf(stderr, "%s\n", tag);
    exit(1);
}

Fixes include:

Testing for I/O errors
Add tag to display function
Use display function copiously
Add error exit function and use it
Primary fix: handle test in while loop in insert() correctly:
- Test temp->link for nullness
- Use && and not || in testing for validity
Improve printing in display() (only output + when it separates two terms; output newline at end)
Don't leak memory in main().
Don't pass uninitialized memory to create().
Don't ignore return from create().

Example run:

enter the first polynomial:
enter the number of nodes: 3
enter the coefficient and exponent respectively: 2 2
after input: 2 x ^ 2
enter the coefficient and exponent respectively: 3 1
insert: p   = : 2 x ^ 2
insert: ptr = : 3 x ^ 1
insert: post loop: 2 x ^ 2
after input: 2 x ^ 2 + 3 x ^ 1
enter the coefficient and exponent respectively: 4 0
insert: p   = : 2 x ^ 2 + 3 x ^ 1
insert: ptr = : 4 x ^ 0
insert: post loop: 2 x ^ 2 + 3 x ^ 1
after input: 2 x ^ 2 + 4 x ^ 0 + 3 x ^ 1
enter the second polynomial:
enter the number of nodes: 5
enter the coefficient and exponent respectively: 1 0
after input: 1 x ^ 0
enter the coefficient and exponent respectively: 2 1
insert: p   = : 1 x ^ 0
insert: ptr = : 2 x ^ 1
after input: 2 x ^ 1 + 1 x ^ 0
enter the coefficient and exponent respectively: 4 6
insert: p   = : 2 x ^ 1 + 1 x ^ 0
insert: ptr = : 4 x ^ 6
after input: 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0
enter the coefficient and exponent respectively: 3 2
insert: p   = : 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0
insert: ptr = : 3 x ^ 2
insert: tmp = : 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0
insert: tmp = : 2 x ^ 1 + 1 x ^ 0
insert: post loop: 1 x ^ 0
after input: 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0 + 3 x ^ 2
enter the coefficient and exponent respectively: 9 3
insert: p   = : 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0 + 3 x ^ 2
insert: ptr = : 9 x ^ 3
insert: tmp = : 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0 + 3 x ^ 2
insert: tmp = : 2 x ^ 1 + 1 x ^ 0 + 3 x ^ 2
insert: tmp = : 1 x ^ 0 + 3 x ^ 2
insert: post loop: 3 x ^ 2
after input: 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0 + 3 x ^ 2 + 9 x ^ 3
p1: 2 x ^ 2 + 4 x ^ 0 + 3 x ^ 1
p2: 4 x ^ 6 + 2 x ^ 1 + 1 x ^ 0 + 3 x ^ 2 + 9 x ^ 3

There is room to think the ordering by exponent is not working correctly, but the code doesn't crash. Running with valgrind spots no memory access errors; it leaks like the proverbial sieve, though.

score 0 · Answer 2 · edited Jun 11 '16 at 10:36

I hope it helps you out.You need to reduce some of the redundancies though.

#include <iostream>
using namespace std;
typedef struct node
{
    int coef,exp;
    node* next;
};
node* start;
node* start1;
node* start2;
node* beg=NULL;
node*begmer=NULL;
void newpol(int);
void display(); 
void merger();
node * allocate(int n)
{
    node* new_node=new node;
cout << "\n Enter the coefficient:";
cin>> new_node->coef;
new_node->exp=n;
new_node->next=NULL;
if(start==NULL)
    {
        start=new_node;
        beg=start;
    }
    else
    {
        start->next=new_node;
    }
    return new_node;
}
int main()
{

    char c='y';
    do
    {
        int ch;
        cout<< "\n Enter your choice: \n 1. Create new expression \n 2. Merge two expression";
        cin >>ch;
        switch(ch)
        {
        case 1:
            int n;
            cout<< "\n Enter the order of polynomial: ";
            cin>>n;
            newpol(n);
            display();
            break;
        case 2:
            merger();
            beg=begmer;
            cout<<"\n After merging::\t";
            display();
            break;}
        cout<< "\n more??";
        cin>>c;
    }while(c!='n');
}
void newpol(int n)
{start=NULL;
    int c=n;
    cout<<"\n for order "<<n<<" polynomial:";
    while(c>=0)
    {
        start=allocate(c);
        c--;
    }
}
void display()
{
    node* temp=new node;
    temp=beg;
    cout<<"\n";
    do{
        cout <<"+

 "<<temp->coef<<" X^ "<<temp->exp;
        temp=temp->next;
    }while (temp!=NULL);
}
void merger()
{
        node* startmerge=NULL;
    int n1,n2;
    cout<<"degree of first and sec:";
    cin >>n1>>n2;
    newpol(n1);
    start1=beg;
    display();
    newpol(n2);
    start2=beg;
    display();
    do{
    node* new_node=new node;
    if (start1->exp==start2->exp)
    {
        new_node->exp=start1->exp;
        new_node->coef=start1->coef+start2->coef;
        start1=start1->next;
        start2=start2->next;
    }
    else if (start1->exp>start2->exp)
    {
        new_node->exp=start1->exp;
        new_node->coef=start1->coef;
        start1=start1->next;
    }
    else if (start1->exp<start2->exp)
    {
        new_node->exp=start2->exp;
        new_node->coef=start2->coef;
        start1=start2->next;
    }
     if (startmerge==NULL)
                    {
                        startmerge=new_node;
                        begmer=startmerge;
                    }
                    else{
                        startmerge->next=new_node;
                        startmerge=startmerge->next;
                    }
    }while(start1&&start2);
}

Hmmm…using a C++ solution for a question tagged C is not the best choice in the world. — Jonathan Leffler, Jun 05 '17 at 18:18

Creating a polynomial with a linked list in C

2 Answers2