Thread: what could the problem be?

Ok when I run my program I test 23+. It suppose to be converted to 2+3 and the answer should be 5. But when I run it it gives me the answer 2. Im not sure what the problem is. Ive use the debugger but Im not figuring out why I get 2.

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) != '\0'){
			if(Operand(s.at(i))){
				S.push(Operand(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;
}

Because the only thing you're pushing onto your stack is "true". You need to push the value of the thing, not "true" or "false" like you get from Operand().

So you are saying I need an if statement?

You have an if statement. I'm saying that this:

Code:

S.push(Operand(s.at(i)));

is desperately wrong. You need to turn that character into a number, not into a bool.

Ok well I changed it to this:

Code:

S.push(s.at(i));

But now here is whats weird. If you use subtraction the value comes out correct but if you use any other operator you wont get the right value.

You need to turn that character into a number. In your example:

s.at(i) = 50 (ASCII '2')
Operand(s.at(i)) = 1 (bool true)

Neither of those is 2. So you're going to have to get 2 out of this character.

ok so I need to add something somewhere that converts the character into a number is that correct? Or is it something Im doin wrong with like in post #4 where Im pushing a character and not a number?

You need to do something to turn '2' into 2, yes. If you can promise "always a single digit", then you can subtract '0' to get 2. If you have numbers >10, then you will have to work harder.

ok I tried this but this does nothing. So is there any suggestions?

Code:

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(Operand(s.at(i))){
				s.at(i) - '0';				
                     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;
}

I've forgotten. Is it a stack of floats or a stack of chars? If it's a stack of chars, then you need to push the letter, and then subtract the '0' when you pop. If it's a stack of floats, you need to push the value of s.at(i) - '0' (as opposed to pushing the character as you are now).