Thread: register bug

Hey guys, I'm having a little bit of trouble with a register I'm making. I'm having an error in the build. Also as I'm very new to c++ if you see anything that I can improve on, such as syntax, etc. please tell me as I wish to form good habits. btw, I'm using code blocks if it makes any difference.
Heres head.hpp

Code:

#include <iostream>

class My_reg
{
    public:
        My_reg(float amount);    //enters amount
        ~My_reg();
        void set_tax();      // declares tax func
        void start_up() const {sub = amount;}
        float sub_total() const {return sub;}   // returns sub_total amount
        float get_total() const {return sub;}  // return sub after tax
        float get_change(float cash);      // declares func to get change
    private:
        float sub;
        float tax;
        float cash;
        float change;
};

source

Code:

#include "head.hpp"

My_reg::My_reg(float amount)
{
    sub = amount;
    float tax = 0.05;
}
My_reg:: ~My_reg()
{
}
void My_reg:: set_tax()
{
    sub = sub + sub * tax;   //adds tax
}
float My_reg:: get_change(float cash)
{
    change = (cash - sub);   /// This is supposed to take how much they gave
    return change;               // and subtract from sub, this is after sub has been through set_tax
}
int main()
{
	std::cout << "Please enter the amount:";
	std::cin >> amount;
	My_reg reg(amount);
	start_up();
	std::cout << "Your sub-total is:" << reg.sub_total();
	reg.set_tax();
	std::cout << "/nYour total is:" << reg.get_total();
	std::cout << "/n Please enter the amount paid:";
	std::cin >> cash;
	std::cout << "Your change is:" << reg.get_change();
	std::cout << "/n/tThank you and have a wonderful day";


	return 0;
}

Thank you for any help && || tips.

Joe

Thank you for your help. I fixed the tax var so it's declared in constructor, as well is sub. Also it seemed to help with the debug that i changed the vars to not match their function ID. Is this correct?
Also I added a few more things and debugged it to about here. // I edited the code above to save space.


Thanks again,

Joe

One last tip, unless you've been instructed otherwise, you should prefer double rather than float. It has better precision and is the default floating point type in C++.

No, I'm not restricted to anything as I'm a hobbyist.(Though I want too keep good habits, and not set myself up later) But I have a book that I'm going by, and on this little "cheat sheet" it gave me, it says that a double is 8 bytes, and stores2.2e-308 to 1.8e-308. I guess that I thought that was a large number, but apparently not. Could you maybe explain what that means? Thanks

No, I'm not restricted to anything as I'm a hobbyist.(Though I want too keep good habits, and not set myself up later) But I have a book that I'm going by, and on this little "cheat sheet" it gave me, it says that a double is 8 bytes, and stores2.2e-308 to 1.8e-308. I guess that I thought that was a large number, but apparently not. Could you maybe explain what that means? Thanks

Wikipedia's article on Floating Points.
double is essentially a better float - it has more range, and better precision. It also takes up more space, but the extra space needed is insignificant.

1.

Code:

    float tax = 0.05;

You're declaring a variable here that is different to the one in your class. It is destroyed when the constructor finishes and the value 0.05 is lost. You need to take away the word 'float' there.
However you should be using "constructor initialiser lists" anyway, so google that.

2. Don't declare or define a destructor if you aren't going to put code in it. The default destructor that the compiler generates for you will do the same thing.

3.

Code:

    sub_total = sub_total + sub_total * tax;   //adds tax

This is the same as

Code:

    sub_total *= (1 + tax);   //adds tax

Which I'd certainly go for.

4. The member variable 'change' doesn't need to be a class member variable because you don't use it outside of the one function. Declare it locally instead if necessary. However get_change could just return the result of the calculation as a one-liner with no need to declare any extra variables.

5. sub_total and get_total are identical. Is there any point in declaring both?

6.

Code:

        void start_up() const {sub = amount;}

That won't compile because there is no identifier called 'amount' that is visible to that function.

7.

Code:

	start_up();

Wont compile either as there is no global function with that name. You can remove this line.