Can't decode a polynomial properly - c

Question

#include<stdio.h>
#include<stdlib.h>
#define TRUE 1
#define FALSE 0
typedef struct polynomial{
int coeff;
char var;
int exp;
struct polynomial *link;
} poly;
poly* decode(char*);
main()
{
char polynomial[100];
poly *first, *second;
printf("\n---Enter 1st polynomial---\n\n");
scanf("%s",polynomial);
first=decode(polynomial);
printf("\n---Enter 2nd polynomial---\n\n");
scanf("%s",polynomial);
second=decode(polynomial);
//More statements further
return 0;
}
/*--- Decoding Polynomial ---*/
poly* decode(char *polynomial)
{
poly *p=NULL, *q=NULL, *temp=NULL;
int i=0, sign;
short coeff_entry=TRUE, exp_entry=FALSE, var_visited=FALSE, exp_visited=FALSE, coeff_visited=FALSE;
while(polynomial[i]!='\0')
{
temp=(poly*)malloc(sizeof(poly));
if(!temp)
{
printf("Error! Memory not allocated\n");
exit(1);
}
if(polynomial[i]==43) {i++; sign=1;}
if(polynomial[i]==45) {i++; sign=-1;}
while(1)
{
if((polynomial[i]>=48&&polynomial[i]<=57)&&coeff_entry==TRUE)
{
temp->coeff=10*(temp->coeff)+(polynomial[i]-48);
coeff_visited=TRUE;
}
else if((polynomial[i]>=65&&polynomial[i]<=90)||(polynomial[i]>=97&&polynomial[i]<=122))
{
temp->var=polynomial[i];
coeff_entry=FALSE;
exp_entry=TRUE;
var_visited=TRUE;
}
else if((polynomial[i]>=48&&polynomial[i]<=57)&&exp_entry==TRUE)
{
temp->exp=10*(temp->exp)+(polynomial[i]-48);
exp_visited=TRUE;
}
else if(polynomial[i]==43||polynomial[i]==45||polynomial[i]=='\0')
{
exp_entry=FALSE;
coeff_entry=TRUE;
if(var_visited&&!exp_visited)
{
temp->exp=1;
!var_visited;
!exp_visited;
}
if(!coeff_visited)
{
!coeff_visited;
temp->coeff=1;
}
temp->coeff*=sign;
break;
}
i++;
}
//These lines are for debugging purpose only
printf("\nCoefficient of the term is: %d\n",temp->coeff);
printf("Variable of the term is: %c\n",temp->var);
printf("Exponent of the term is: %d\n",temp->exp);
temp->link=NULL;
if(p==NULL) p=q=temp;
else
{
q->link=temp;
q=q->link;
}
}
return p;
}
In my code I am asking user to input a polynomial in the form like: -5x^2+7y^3-19z+5
Everything seems fine but two problems in decoding this polynomial and storing in the linked list form:
First bug comes when the first-most coefficient is positive in polynomial like 17x^3-13z+5
In this case a very long integer value (most probably garbage value) gets store in the respected node of linked list.
Second bug is when there is no first coefficient like x^7-18y^3+z-13
In this case 0 gets stored in the respected node of linked list. In other terms of polynomial, like z in example above, where there is no coefficient 1 gets stored in the coeffient part of the node.
So problem arises with the first coefficient only that too a 'positive coeff' or 'no coefficient' at all.

Answer 1

There are many errors in your code, the most important is the expresions like
!value;
you need to assign to it, lik
value = !value;
And you are not initializing sign when there is not '+' sign in front of the next token, you need to initialize it to 1, check if there is a '-' and set it to -1 otherwise ignore the '+'.
Now I appended the fixed code, try it
#include <stdio.h>
#include <stdlib.h>
#define TRUE 1
#define FALSE 0
typedef struct _polynomial {
int coeff;
char var;
int exp;
struct _polynomial *link;
} poly;
poly *decode(char*);
int
main()
{
char string[100];
printf("\n---Enter 1st polynomial---\n\n");
scanf("%99s", string);
decode(string);
printf("\n---Enter 2nd polynomial---\n\n");
scanf("%99s", string);
decode(string);
//More statements further
return 0;
}
/*--- Decoding Polynomial ---*/
poly* decode(char *polynomial)
{
poly *p = NULL, *q = NULL, *temp = NULL;
int i = 0, sign;
short coeff_entry=TRUE, exp_entry=FALSE, var_visited=FALSE, exp_visited=FALSE, coeff_visited=FALSE;
while (polynomial[i] != '\0')
{
temp = malloc(sizeof(poly));
if (temp == NULL)
{
printf("Error! Memory not allocated\n");
exit(1);
}
sign = 1;
if (polynomial[i] == 43)
i++;
if (polynomial[i] == 45)
{
i++;
sign=-1;
}
while (1)
{
if ((polynomial[i] >= 48 && polynomial[i] <= 57) && coeff_entry == TRUE)
{
temp->coeff = 10 * temp->coeff + polynomial[i] - 48;
coeff_visited = TRUE;
}
else if ((polynomial[i] >= 65 && polynomial[i] <= 90) || (polynomial[i] >= 97 && polynomial[i] <= 122))
{
temp->var = polynomial[i];
coeff_entry = FALSE;
exp_entry = TRUE;
var_visited = TRUE;
}
else if ((polynomial[i] >= 48 && polynomial[i] <= 57) && exp_entry == TRUE)
{
temp->exp=10*(temp->exp)+(polynomial[i]-48);
exp_visited=TRUE;
}
else if (polynomial[i] == 43 || polynomial[i] == 45 || polynomial[i] == '\0')
{
exp_entry=FALSE;
coeff_entry=TRUE;
if (var_visited && !exp_visited)
{
temp->exp = 1;
var_visited = !var_visited;
exp_visited = !exp_visited;
}
if (!coeff_visited)
{
coeff_visited = !coeff_visited;
temp->coeff = 1;
}
temp->coeff *= sign;
break;
}
i++;
}
printf("\nCoefficient of the term is: %d\n", temp->coeff);
printf("Variable of the term is: %c\n", temp->var);
printf("Exponent of the term is: %d\n", temp->exp);
temp->link = NULL;
if (p == NULL)
p = q = temp;
else
{
q->link = temp;
q = q->link;
}
}
return p;
}