Program to solve equations using double linked list

Mon Jul 20, 2009 10:52 pm

Hi,
I am having trouble with a c++ program I am trying to write. The program should be able to solve equations like "3 / ( 4 * 5 ) =" however when i run it a get a runtime error (Unhandled exception). The program is not entirely finished but I can't continue untill i figure this out. It must use a doubly linked list. I am a beginning programmer so please take the time to explain everything, and stick with the simplist code.

Thanks for your time.

Code:: //program needs to be able to solve equations like 3 / ( 4 * 5 ) = //note: when imputing equation, separate each character with a space and end it with a â€œ=â€ //when I run the program, I get a runtime error â€“ not sure why #include <iostream> #include <string> using namespace std; struct node { node * prev; int value; char op; char type; node * next; }; void printlist (node *h); void mult (node * right, node * left); void main ( ) { char str[15]; node * dll, *head, *tail, *rp, *lp; cout << "Enter equation: " << endl; cin >> str; dll = new node; head = dll; tail = dll; head ->prev = 0; head -> op = '('; head -> type = 'o'; head -> value = -1; while (str[0] != '=') //check for end of expression, doesn't include = sign. Loop will get all imput and put it into a doubly linked list. { if (isdigit(str[0])) { tail->next = new node; tail->next->prev = tail; tail = tail->next; tail->value= atoi(str); tail->type='n'; tail->op='$'; } else { tail->next = new node; tail->next->prev = tail; tail = tail->next; tail ->op = str[0]; tail->type='o'; tail->value=-1; } cin >> str; } tail->next = new node; tail->next->prev = tail; tail = tail->next; tail->next=0; tail->op=')'; tail->type='o'; tail->value=-1; printlist (dll); //while (dll->op == '(') //{ rp = head; while (rp->op != ')') rp = rp -> next; lp = rp; while (lp->op != '(') lp = lp -> prev; cout << "lp: " << lp << " rp: " << rp; mult (rp, lp); printlist (dll); //} system("pause"); } //Following function used for testing purposes void printlist (node *h) { while ( h != 0) { cout << " prev: " << h->prev << " addr: " << h <<" value: " << h->value << " op: " << h->op << " type: " << h->type<< " address of next node: " << h->next << endl; h=h->next; } cout << endl; } void mult (node * right, node * left) { node * temp; temp = left; cout <<endl<< "Left: " << left << " Right: " << right << " Temp: " << temp << " Temp->op: " << temp->op; system("pause"); while (temp != right) { while ((temp->op != '*') || (temp->op != '/') ) temp = temp ->next; if (temp -> op == '*') { temp->value = temp->prev->value * temp->next->value; //computes temp->prev->prev->next= temp->next->next; //deletes extra numbers } if (temp -> op == '/') { temp->value = temp->prev->value * temp->next->value; temp=temp->prev->prev->next;//not correct? temp=temp->next->next->prev;//not correct? } } return; }

Wed Jul 22, 2009 5:35 pm

what exactly you want to create a calculator withc solves arithmetic combinations of a kind ..or something exact such as 3/(5*4) ?? you only want to be able to pick up the numbers or what i was looking the lines of your code the 2 last lines temp = ...etc definatly rong

cout << " prev: " << h->prev << " addr: " << h <<" value: " << h->value << " op: " << h->op << " type: " << h->type<< " address of next node: " << h->next << endl;

hear what is going on .? too many pointers..

)))

Program to solve equations using double linked list

Program to solve equations using double linked list

Re: Please help me with my code!