Thread: Help with my project 2

Write a program in C++ that evaluates portfix strings (one per line in a text file) with the following restrictions on the input: Each character is either an operand- if it is a digit and the floating point value associated with the digit, or it is one of the 5 binary operators: +, -, *, / (floating point), ^ (exponentiation). You must use a stack, in particular, the linked list implementation of the stack.

I dont know how to go about this!

Please post the your code of what you have tried.


Please don't open a new post for each question on the same topic.


Jim

Is there anything you notice that is incorrect about this?

Code:

#include<iostream>
#include<stack>
using namespace std;

class Lstack {
private:
	char Link *top;	/*Pointer to first element*/
	int size;	/*Count number of elements*/
public:
	Lstack(int sz =DefaultListSize) {top = NULL; size = 0;}
	~Lstack() {clear();}	/*Destructor*/
	void clear() {
		while (top != NULL) { /*Delete link nodes*/
			Link* temp = top;
			top = top->next;
			delete temp;
		}
		size = 0;
	}
	bool push(const Elem& item) {
		top = new Link(item, top);
		size++;
		return true;
	}
	bool pop(Elem& item) {
		if(size == 0) return false;
		it = top->element;
		Link *ltemp = top->next;
		delete top;
		top = ltemp;
		size--;
		return true;
	}
	bool topValue(Elem& it) const {
		if (size ==0) return false;
		it = top->element;
		return true;
	}
	int length() const {return size;}
	bool isEmpty() const {
		if (top == NULL) return true;
		else return false;
	};
int main(){
	return 0;
}

Code:

Lstack(int sz =DefaultListSize) {top = NULL; size = 0;}

If you're passed the size, wouldn't you really like to use the size?

Why have boolean methods that never return anything but true?

Shouldn't pop, actually, well...pop something?