What is wrong with my addition of polynomials c code? -

i wrote c program should add 2 polynomials. wrote program in kali linux 2.0 os. when execute program don't required output. instead this-

polynomial 1  how many no. terms want enter? 1  enter coefficient term 1: 2 enter exponent term 1: 3  polynomial 2  how many no. terms want enter? 1  enter coefficient term 1: 2 enter exponent term 1: 3   polynomial 1= polynomial 2= sum of 2 polynomials 

the program code given below-

#include<stdio.h> #include<stdlib.h>  typedef struct node {     int exp,coeff;     struct node *next; }poly;  poly *heada,*headb,*headc; poly *lasta,*lastb,*lastc;  void insert(poly*,poly*,poly *); void input(poly *,poly *); void display(poly *);  void insert(poly *new,poly *head,poly *last) {     poly *p,*q;     if(head==null&&last==null)  //setting start     {         head=last=new;         return;     }     p=head;     q=null;     while(new->exp<p->exp)       {         q=p;         p=p->next;     }     if(p->exp==new->exp)    //if exponents equal         p->coeff=p->coeff+new->coeff;     else     {         if(q!=null) //insertion in middle         {             q->next=new;             new->next=p;         }         else if(q==null)    //insertion @ beginning         {             new->next=head;             head=new;         }         else if(p==null)    //insertion @ end         {             last->next=new;             last=new;         }     } }  void input(poly *head,poly *last) {     int i,n,c,e;     poly *new;     new=(poly *)malloc(sizeof(poly));     printf("how many no. terms want enter? ");     scanf("%d",&n);     for(i=1;i<=n;i++)     {         printf("\nenter coefficient term %d: ",i);         scanf("%d",&new->coeff);         printf("enter exponent term %d: ",i);         scanf("%d",&new->exp);         new->next=null;         insert(new,head,last);         insert(new,headc,lastc);     } }  void display(poly *start) {     poly *p;     p=start;     while(p!=null)     {         printf("(%dx^%d)+",p->coeff,p->exp);         p=p->next;     }     printf("\b"); }  void main() {     system("clear");      heada=(poly *)malloc(sizeof(poly));     headb=(poly *)malloc(sizeof(poly));     headc=(poly *)malloc(sizeof(poly));     lasta=(poly *)malloc(sizeof(poly));     lastb=(poly *)malloc(sizeof(poly));     lastc=(poly *)malloc(sizeof(poly));      heada=headb=headc=null;     lasta=lastb=lastc=null;      printf("polynomial 1\n\n");     input(heada,lasta);     printf("\npolynomial 2\n\n");     input(headb,lastb);     printf("\n\npolynomial 1=");     display(heada);     printf("\npolynomial 2=");     display(headb);     printf("\nsum of 2 polynomials is=");     display(headc); } 

edit: after reading comments brought changes in code. output is-

polynomial 1  how many no. terms want enter? 1  enter coefficient term 1: 5 enter exponent term 1: 6  polynomial 2  how many no. terms want enter? 2  enter coefficient term 1: 6 enter exponent term 1: 5  enter coefficient term 2: 7 enter exponent term 2: 8   polynomial 1=(0x^0)+ polynomial 2=(0x^0)+ sum of 2 polynomials is=(0x^0) 

the present program code is-

poly *insert(poly*,poly*,poly *); poly *input(poly *,poly *); void display(poly *);  poly *insert(poly *new,poly *head,poly *last) {     poly *p,*q;     if(head==null&&last==null)     {         head=last=new;         return;     }     p=head;     q=null;     while(new->exp<p->exp)     {         q=p;         p=p->next;     }     if(p->exp==new->exp)         p->coeff=p->coeff+new->coeff;     else     {         if(q!=null)         {             q->next=new;             new->next=p;         }         else if(q==null)         {             new->next=head;             head=new;         }         else if(p==null)         {             last->next=new;             last=new;         }     }     return head; }  poly *input(poly *head,poly *last) {     int i,n,c,e;     poly *new;     printf("how many no. terms want enter? ");     scanf("%d",&n);     for(i=1;i<=n;i++)     {         new=(poly *)malloc(sizeof(poly));         if(new==null)         {             printf("allocation error!!");             break;         }         printf("\nenter coefficient term %d: ",i);         scanf("%d",&new->coeff);         printf("enter exponent term %d: ",i);         scanf("%d",&new->exp);         new->next=null;         head=insert(new,head,last);         headc=insert(new,headc,lastc);         free(new);     }     return head; }  void display(poly *start) {     poly *p;     p=start;     while(p!=null)     {         printf("(%dx^%d)+",p->coeff,p->exp);         p=p->next;     }     printf("\b"); }  void main() {     system("clear");      heada=(poly *)malloc(sizeof(poly));     headb=(poly *)malloc(sizeof(poly));     headc=(poly *)malloc(sizeof(poly));     lasta=(poly *)malloc(sizeof(poly));     lastb=(poly *)malloc(sizeof(poly));     lastc=(poly *)malloc(sizeof(poly));      if(heada==null||headb==null||headc==null||lasta==null||lastb==null||lastc==null)     {         printf("allocation failure!!!");         return;     }      heada=headb=headc=null;     lasta=lastb=lastc=null;      printf("polynomial 1\n\n");     heada=input(heada,lasta);     printf("\npolynomial 2\n\n");     headb=input(headb,lastb);     printf("\n\npolynomial 1=");     display(heada);     printf("\npolynomial 2=");     display(headb);     printf("\nsum of 2 polynomials is=");     display(headc); } 

here's working version:

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

a term_t describes single term in polynomial.

typedef struct term {     int exp;     int coeff;     struct term *next; } term_t; 

a poly_t describes whole polynomial, list of terms. last pointer wasn't necessary since traverse list start.

typedef struct poly {     term_t *head; } poly_t; 

we need way initialize polynomials setting list of terms empty. need way destroy polynomial freeing of terms.

void init_poly(poly_t *poly) {     poly->head = null; }  void destroy_poly(poly_t *poly) {     term_t *term = poly->head;     while (term != null) {         term_t *nextterm = term->next;         free (term);         term = nextterm;     }     poly->head = null; } 

we find necessary able clone term (create copy of existing term). note in c, not necessary cast return value of malloc.

term_t *clone_term(term_t *term) {     term_t *new_term;      if ((new_term = malloc(sizeof *new_term)) == null) {         printf("allocation failure!!!\n");         return null;     }      new_term->coeff = term->coeff;     new_term->exp = term->exp;     new_term->next = null;     return new_term; } 

we need way insert term polynomial. terms kept sorted exponent (highest exponent comes earlier in list), if term matching exponent in polynomial, add coefficient. can eliminate of special-case code maintaining pointer next pointer modify point new term.

void insert_term(poly_t *poly, term_t *term) {     term_t **nextptr = &poly->head;     term_t *nextterm;      while ((nextterm = *nextptr) != null) {         if (nextterm->exp == term->exp) {             /* found existing term matching exponent */             nextterm->coeff += term->coeff;             free (term); /* don't need term must free'd */             return;         }         else if (nextterm->exp < term->exp) {             /* next term has lower exponent, stop here */             break;         }         nextptr = &nextterm->next;     }      term->next = nextterm;     *nextptr = term; } 

the input_poly function responsible inputting single polynomial. allocates new term_t each term inserts.

int input_poly(poly_t *poly) {     int i, n;      printf("how many terms want enter? ");     scanf("%d", &n);      (i = 0; < n; i++) {         term_t *term;          if ((term = malloc(sizeof *term)) == null) {             printf("allocation failure!!!\n");             return -1;         }          printf("\nenter coefficient term %d: ", i+1);         scanf("%d", &term->coeff);          printf("enter exponent term %d: ", i+1);         scanf("%d", &term->exp);          term->next = null;          insert_term(poly, term);     }      return 0; } 

the add_to_poly function adds polynomial existing polynomial. cloning terms of addend, , inserting them accumulator. necessary clone each term because term cannot member of 2 polynomials @ same time. note since exponents of both polynomials kept in sorted order, done more efficiently.

int add_to_poly(poly_t *accum, const poly_t *addend) {     term_t *term;     (term = addend->head; term != null; term = term->next) {         term_t *new_term;          if ((new_term = clone_term(term)) == null) {             return -1;         }          insert_term(accum, new_term);     }      return 0; } 

using backspace character delete trailing + may appear work on terminal, not work when output redirected file. better print separator when needed.

void display_poly(poly_t *poly) {     term_t *term;     (term = poly->head; term != null; term = term->next) {         printf("(%dx^%d)", term->coeff, term->exp);         if (term->next != null) {             printf("+");         }     } } 

main supposed have following type signature. initialize our polynomials, input 2 polynomials, add them , print them.

int main(int argc, char **argv) {     poly_t polya;     poly_t polyb;     poly_t polyc;      init_poly(&polya);     init_poly(&polyb);     init_poly(&polyc);      printf("polynomial 1\n\n");     if (input_poly(&polya) == -1) {         goto error;     }     printf("\n");      printf("polynomial 2\n\n");     if (input_poly(&polyb) == -1) {         goto error;     }     printf("\n\n");      if ((add_to_poly(&polyc, &polya) == -1 ||          add_to_poly(&polyc, &polyb) == -1)) {         goto error;     }      printf("polynomial 1=");     display_poly(&polya);     printf("\n");      printf("\npolynomial 2=");     display_poly(&polyb);     printf("\n");      printf("\nsum of 2 polynomials is=");     display_poly(&polyc);     printf("\n");  error:     destroy_poly(&polya);     destroy_poly(&polyb);     destroy_poly(&polyc);      return 0; }