Problem with classes

[enrica cabrino]

what is a class?

[Ganado]

What is your question?

[enrica cabrino]

write the methods of the Class Line:

bool vertical();
bool horizontal();
double slope();
bool parallel(Line r);
Point intersection(Line r);

[Ganado]

That is... not a question.

You are being given lines in Standard Form, Ax + By = C.
I would suggest reading an article such as this: http://courses.wccnet.edu/~palay/precalc/22mt01.htm
It seems to explain the basics pretty well.

Your first two methods are determining whether or not a line is vertical or horizontal, respectively.
To tackle this, you first need to know what a vertical line looks like in standard form.

An example of a vertical line is x = 4. Notice that it doesn't depend on y at all.
An example of a horizontal line is y = 3. Notice that it doesn't depend on x at all.
From this, we can deduce that if a line doesn't depend on y, then B must be equal to 0:
1x + 0y = 4 --> 1x = 4
If a line doesn't depend on x, then A must be equal to 0:
0x + 1y = 3 --> 1y = 3

From this, we can conclude that if a line is vertical, B = 0, and if a line is horizontal, A = 0.

Do you know how to write this statement in code? I'll start it off for you.

bool Line::vertical()
{
    if ( /* B is equal to 0 */)
        return true;
    else
        return false;
}

For completeness, you would also check for the degenerate form where both A and B are equal to 0, which is not a valid line. But I wouldn't worry about that for now.

__________________

To get the slope of a line in standard form, Ax + By = C,
you need to tranform it into slope-intercept form, y = mx + b (note: lowercase b is not the same as B).
m is then the slope, and b is the y-intercept.

Ax + By = C
By = C - Ax
y = (C/B) - (A/B) x
y = -(A/B)x + (C/B)
The slope is -A/B.

[enrica cabrino]

The theory is very clear to me. My problem is just building the c ++ file

[enrica cabrino]

Could you complete all the methods exhaustively, please? Thank you so much.

[Ganado]

You need to put in methods that implement vertical, horizontal, slope, parallel, and intersection.

I'll start you off with a bit more. Insert this code after the definition of your class, but before main().

bool Line::vertical()
{
    return false;
}

bool Line::horizontal()
{
    return false;
}

double Line::slope()
{
    return 0.0;
}

bool Line::parallel(Line r)
{
    return false;
}

Point Line::intersection(Line r)
{
    Point p;
    return p;
}

You also need to provide a definition for the constructor. Do you know how to write a constructor?

Line::Line(double A, double B, double C)
: a_param(A), b_param(B), c_param(C) {} 

Now you need to fill in the functions with actual logic.
e.g.

bool Line::vertical()
{
    return b_param == 0;
}

[dhayden]

Could you complete all the methods exhaustively, please?

Programming is a lot like football: you have to practice. You're going to have to knuckle down and write some code yourself.

[enrica cabrino]

VERY USEFUL.......

[keskiverto]

What is this "class" thingy of C++?

http://www.cplusplus.com/doc/tutorial/classes/
http://en.cppreference.com/w/cpp/language/classes
http://en.cppreference.com/w/cpp/language/class
http://en.cppreference.com/w/cpp/language/member_functions
https://en.wikipedia.org/wiki/C%2B%2B_classes

[Ganado]

keskiverto FYI the OP deleted their original post.

[keskiverto]

Ahh, that explains why the responses did not quite match the (current version of) OP:

what is a class?

[jonnin]

The 10 cent answer is that a class is a user defined type, much like 'int' or 'double'.

The language provides many classes for you, such as std::string, or std::vector, etc.

There is a LOT more to it when talking about object oriented programming designs and techniques, but at the beginner level, a class is just a type that can be used to create variables (objects) of your new custom type.

The first thing a beginner will see in classes is that it organizes code nicely.
consider your line program... you need m, x, and b to define a line in one of its formats, 3 variables. If you just define them in main (double x,m,b) they don't really have anything that ties them together as a 'thing'. If you want to do something like plot your line, you need to do something like plot(m,x,b); If you had a class that contains m,x,b inside, then that becomes myline.plot() and the m,x,b variables are removed from main where they are clutter. Now imagine you had 10 lines. In example 1 you now need in main m1,m2,m3,m4, ... x1,x2,x3,.. etc and its a huge mess. With the class, you just need line1, line2, ... of course you can manage either lines or m/x/bs in a vector or something, but the effort reduction to manage things is still huge. You will see many other benefits as you learn more.