Thread: converting to float

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.

Right now Im just tryna get postfix strings with 3 characters like 42-, 23+, 32^, 12*, and 93/. Only my subtraction works. I need to convert the characters into floats but I dont know how to do that and I cant find it in any books.

Code:

#include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
using namespace std;

const int DefaultListSize =50;
typedef float Elem;

class Link {
public:
	Elem element;	/*Value for this node*/
	Link* next;		/*Pointer to the next node in list*/
	Link(const Elem& elemval, Link* nextval =NULL)
	{ element = elemval; next = nextval; }
	Link(Link* nextval =NULL) { next = nextval; }
};

class Lstack {
private:
	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;
		item = 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;
	}
};
	bool Operand(float ch){
		if(('0' <= ch) && (ch <= '9'))
			return true;
		else return false;
	}

	bool Operator(char ch){
		if((ch == '+') || (ch =='-')|| (ch == '*') || (ch == '/') || (ch == '^'))
			return true;
		else return false;
	}

	float Eval(float oprndL, char oper, float oprndR);
	
int main(){

	Lstack S;
	string s;
	float a = 0;
	char b = 0;
	float c = 0;
	float answer;
	unsigned int i;
	
	cout << "Enter Postfix string:\n";
	getline(cin, s);

	for(i=0; i < s.length(); i++ ){
		if(s.at(i) != EOF){
			if(Operand(s.at(i))){
				S.push(s.at(i));
			}
			else if(Operator(s.at(i))){
				b = s.at(i);
			}
		}
	}
	if(!S.isEmpty()){
		S.pop(c);
		S.pop(a);
		Eval(a, b, c);
		S.push(Eval(a, b, c));
		S.pop(answer);
		cout << answer << endl;
	}
	return 0;
}

float Eval(float oprndL, char oper, float oprndR){
		if(oper == '+') return oprndL + oprndR;
		else if(oper == '-') return oprndL - oprndR;
		else if(oper == '*') return oprndL * oprndR;
		else if(oper == '/') return oprndL / oprndR;
		else if(oper == '^') return pow(oprndL,oprndR);
		else return 0.0;
}

I'm not sure why you think the answer will be different this week than last week, but: you need to subtract '0' from a character (representing a digit) to get the value of that digit.

I didnt think that I couldnt find my original post so I just reposted this. What do you mean by subtract '0' from a character?

What are you talking bout? All I did is post my instructions Im suppose to follow. Since I could not find the original posting I was looking for so I reposted it.