what could the problem be?

This is a discussion on what could the problem be? within the C++ Programming forums, part of the General Programming Boards category; Ok when I run my program I test 23+. It suppose to be converted to 2+3 and the answer should ...

  1. #1
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    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;
    }

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    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().

  3. #3
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    So you are saying I need an if statement?

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    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.

  5. #5
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    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.

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    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.

  7. #7
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    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?

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    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.

  9. #9
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    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;
    }

  10. #10
    and the Hat of Guessing tabstop's Avatar
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    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).

  11. #11
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    "s.at(i) - '0';" obtains the value of s.at(i), subtracts '0' from it, and discards the result. The net result is no visible effect.

    If you actually want to use the value of s.at(i) - '0' you need to do something with it, rather than just discarding it. For example, to save it in the variable b, use "b = s.at(i) - '0';". To print it out (assuming the value is printable) do something like "cout << (b.at(i) - '0');"
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy in reply to you, it is likely you deserve it. Suck it up, sunshine, and read this, this, and this before posting again.

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