I am working on an assignment about pure virtual functions. I have two different classes that i wish to use a pure virtual function. The virtual function is used to calculate area, each class i.e ( square, triangle) use different arguments to calculate the area. How can i make both getArea functions work with the pure virtual function?
#include <iostream>
#include <cmath>
using namespace std;
class Point{
public:
double x, y;
Point(double a = 0, double b = 0){x = a; y = b;}
Point operator + (Point const &obj){
Point p;
p.x = x + obj.x;
p.y = y + obj.y;
return p;
}
Point operator - (Point const &obj){
Point p;
p.x = x - obj.x;
p.y = y - obj.y;
return p;
}
friend ostream& operator<<(ostream& os, const Point& pt);
};
class Shape{
public:
virtual double getArea(Point a, Point b, Point c, Point d) = 0 ; // this is where i have a problem
// need this to be virtual void getArea() = 0; so i can use it for every other class but not sure how
};
class Square: public Shape{
public:
// find area from four points
double length(Point a, Point b){
double hDis = pow((b.x - a.x),2);
double vDis = pow((b.y - a.y),2);
return sqrt(hDis + vDis);
}
double area_triangle(Point a, Point b, Point c){
double A = length(a, b);
double B = length (b, c);
double C = length(a, c);
double S = (length(a, b) + length (b, c) + length(a, c))/2;
double area = sqrt((S*(S-A)*(S-B)*(S-C)));
return area;
}
double getArea(Point a, Point b, Point c, Point d){ // have to calculate area with the point coordinates
double area_tri1 = area_triangle(a, b, c);
double area_tri2 = area_triangle(a, d, c);
double total_area = area_tri1 + area_tri2;
return total_area;
}
};
class Triangle: public Shape{
public:
double length(Point a, Point b){
double hDis = pow((b.x - a.x),2);
double vDis = pow((b.y - a.y),2);
return sqrt(hDis + vDis);
}
double getArea(Point a, Point b, Point c){
double A = length(a, b);
double B = length (b, c);
double C = length(a, c);
double S = (length(a, b) + length (b, c) + length(a, c))/2;
double air = sqrt((S*(S-A)*(S-B)*(S-C)));
return air;
}
};
ostream& operator<<(ostream& os, const Point& pt)
{
os << pt.x << ", " << pt.y <<endl;
return os;
}
int main(){
Point p1(5,-5), p2(-10,7), p3(4, 23), p4(-6, 12);
Square s;
cout << s.getArea(p1, p2, p3, p4);
//! Triangle t;
//! cout << t.getArea(p1, p2,p3);
// this gives me an error because the abstract function want
// (Point a, Point b, Point c, Point d)
// how do i make this work?
}
You've designed your classes a bit strangely.
They should have data members ("member variables") that define their extents (as many Points as you need for that particular type).
Then there is no need to pass any arguments into getArea(): the implementation of this function in each class will use the member variables!
And then you won't have your problem any more, because all of the getArea() functions will have the same number of arguments: none.
If you move things out of function arguments, and into member variables, so that your classes actually contain some state, you should find that the rest of your design falls into place around that change.
Related
I have another problem that I have no idea how to solve. Maybe somebody can help me.
What I want to do:
I have a vector that shall take elements of various class types. In my example code I have two classes (Line, circle) that are both derived from a virtual class segment.
My code shall chain several circle or Line elements and put them in the vector. Each element may be different from the other (different radii, different starting and ending points, etc) and the sequence of elements shall vary from execution to execution. That is for instance for the first execution I have a circle with radius 2 followed by another circle of radius 1, followed by a Line of length 4 and for the second execution I have a Line of length 1 followed by another Line of Length 5 in a different direction, followed by a circle of radius 0.5.
I've already learned how to compose the vector such that it can contain different types but as of now the sequence and definition of each element is hard-coded. Now I want to make this flexible (in the end the sequence and definition shall be file-driven). For this I attempt to implement a template function that takes whatever element is fed into it and adds it to the vector. The current definition also takes the vector as input but I may end up to define this function as a method for the vector.
Unfortunately I cannot figure out a way how to do it that works. I understand that I cannot copy a unique_ptr so I tried with the std::move() method but doesn't work. I get an C2664 error message of the xmemory module in line 671 saying that I cannot convert argument 1 in T2 into a std::nullptr_t.
Can somebody help me here? That'll be so awesome!
Here's my example code that implements the basic idea for my code:
#include <iostream>
#include <vector>
#include <variant>
struct point
{
double x;
double y;
};
class segment
{
public:
segment()
{
P1.x = 0;
P1.y = 0;
P2.x = 0;
P2.y = 0;
};
virtual ~segment() {};
virtual double get_radius() { return 0; };
virtual double get_length() { return 0; };
virtual double get_angle() { return 0; };
int segment_id = 0;
protected:
point P1;
point P2;
};
class Line : public segment
{
public:
Line() {};
Line(const point pt1, const point pt2)
{
P1.x = pt1.x;
P1.y = pt1.y;
P2.x = pt2.x;
P2.y = pt2.y;
segment_id = 1;
};
~Line() {};
double get_length() { return calc_length(); };
double get_angle() { return calc_angle(); };
private:
double calc_length()
{
// calculate length (here: dummy value)
return 1;
}
double calc_angle()
{
// calculate angle (here: dummy value)
return 0.5;
}
double length = 0;
double angle = 0;
}
;
class circle : public segment
{
public:
circle()
{
center.x = 0;
center.y = 0;
};
circle(const double r, const point c)
{
radius = r;
center.x = c.x;
center.y = c.y;
segment_id = 2;
};
~circle() {};
double get_radius() { return radius; };
point get_center() { return center; };
double get_length() { return 3.14 * radius; }; //returns circumference
private:
double radius = 0;
point center;
};
//-------------------------------------------------------
//T1: class type "segment", T2: class object Line or circle
template<typename T1, typename T2>
inline void add_segment(T1 v, T2 line_or_circle)
{
v.emplace_back(line_or_circle);
}
//-------------------------------------------------------
int main()
{
int nbr = 5;
point start;
start.x = 1;
start.y = 2;
point end;
end.x = 3;
end.y = 4;
point c;
c.x = 0;
c.y = 0;
double r = 9;
auto anotherCircle = std::make_unique<circle>(r, c);
auto anotherLine = std::make_unique<Line>(start, end);
circle myCircle(r, c);
//VERSION 1: Does now compile.
std::vector<std::unique_ptr<segment>> v1;
v1.emplace_back(std::move(anotherCircle));
v1.emplace_back(std::move(anotherLine));
std::cout << v1[0]->get_radius() << std::endl;
std::cout << v1[1]->segment_id << std::endl;
//VERSION 2: Compiles
std::vector<std::unique_ptr<segment>> v2;
v2.emplace_back(std::make_unique<circle>(r, c));
v2.emplace_back(std::make_unique<Line>(start, end));
//=================================================================
//now I want to implement this as a function call
//=================================================================
std::vector<std::unique_ptr<segment>> v3;
//VERSION 5:
auto myLine2 = std::make_unique<Line>(start, end);
add_segment(v3, std::move(myLine2)); //shall add object of class Line or circle (derived from virtual segment class, see above) to vector v3. In this example a Line but might be a circle
}
Your function add_segment is taking the vector by value. This fails to compile because the vector is uncopyable, as unique pointers are uncopyable. Even if you used a copyable pointer type, it would be a pointless method as the copy is destroyed at the end of the function.
You will also need to move the line_or_circle parameter in the body of add_segment.
template<typename T1, typename T2>
inline void add_segment(T1 & v, T2 line_or_circle)
{
v.emplace_back(std::move(line_or_circle));
}
I am working on a project for understanding classes and have hit a wall. If you have any advice about my syntax, please let me know where I am going wrong as I am still quite new to programming, but my question is to do with class inheritance. (A, C and D are included but pretty well completed).
My project:
A. Start with a point class... Override << (print values), +, - (to add and subtract point coordinates). I feel I have completed this portion.
B. Create a base class Shape. Shape will contain functions to calculate area, circumference and take point values to create a box that encapsulates the given shape. These will be overloaded by derived classes. Create a display() function that displays all relevant info (name, area, circumference and encapsulating box.
C. Build a heirarchy for shapes by making circle, square, triangle... add default and custom constructors whos arguments initialize the shapes using the correct number of point objects. I feel I have satisfied this too.
D. In main() Create an instance of each. Circle radius = to 23, square sides each = 25, Triangle sides = 10, 20 and 30 (very flat triangle, area = 0). Define each to contain the origin (0, 0). Display all the info. I feel I have completed this (minus the display function).
My question is (and where I am struggling), "How do I properly make/access functions from a base class (shape) to return meaningful information."
Do I literally just make them all virtual since some classes dont have the same information as others? (like Area() and Circumference()?)
#include <iostream>
#include <cmath>
using namespace std;
class Point {
public:
int x, y;
Point() {
x = 0;
y = 0;
}
Point(int x, int y): x(x), y(y) {} // constructor
friend ostream& operator<<(ostream& out, const Point number) { //Involves ostream to output the numbers
out << "(" << number.x << ", " << number.y << ")"; //that were input into the x and y values of Point.
return out;
}
friend Point operator+(Point first, Point second) { //Takes two mathematical vectors and tells the compiler
Point add; // to add the x values together and the y values together
add.x = first.x + second.x;
add.y = first.y + second.y;
return add;
}
friend Point operator-(Point first, Point second) { // same as above but with subtraction.
Point subtract;
subtract.x = first.x - second.x;
subtract.y = first.y - second.y;
return subtract;
}
};
class Shape {
protected:
float height, width;
public:
Shape() {
height = 0;
width = 0;
}
Shape(float h, float w) {
height = h;
width = w;
}
/*
int Display() {
//Do something..... Create a display function
return 0;
}
int BoundingBox() {
//Do something again......
return 0;
}
*/
virtual float Area() const = 0;
virtual float Circumference() const = 0;
virtual ~Shape() {};
};
class Circle: public Shape {
Point center;
float radius;
public:
Circle(): Shape() {};
Circle (Point p1, float r) { //Takes center point object, and given radius.
center = p1;
radius = r;
}
virtual float Area() const override { // Calculates circle area
return(M_PI * radius * radius);
}
virtual float Circumference() const override { // Calculates circumference
return(float (M_PI * 2 * radius));
}
virtual ~Circle() {};
};
class Square: public Shape {
Point first, second, third, fourth;
public:
Square(): Shape() {};
Square(Point p1, Point p2, Point p3, Point p4) { // Takes four point arguments and initializes them
first = p1;
second = p2;
third = p3;
fourth = p4;
height = second.x - first.x; //calculates the height and width from points
width = third.y - first.y;
}
virtual float Circumference() const override {
return 0; //Errors without the return statement
}
virtual float Area() const override{ // Calculates area by measuring the difference between given points
return(height * width);
}
virtual ~Square() {};
};
class Triangle: public Shape {
Point first, second, third;
public:
Triangle(): Shape() {};
Triangle(Point p1, Point p2, Point p3) { // Takes three point arguments and initializes them
first = p1;
second = p2;
third = p3;
height = third.y - first.y;// due to the nature of the question, this only works for flat triangles.
width = second.x - first.x;
}
virtual float Circumference() const override {
return 0; //Errors without the return statement
}
virtual float Area() const override {
return ((height * width) / 2);
}
virtual ~Triangle() {};
};
int main() {
Point p1(0, 0), p2(25, 0), p3(0, 25), p4(25, 25), p5(20, 0), p6(30, 0);
Circle c1 (p1, 23); // Circle with origin (0, 0) and a radius of 23
Square s1 (p1, p2, p3, p4); // Square with 4 points and the origin
Triangle t1 (p1, p5, p6); // Extraordinarily flat triangle with origin
cout << c1.Circumference() << endl;
cout << s1.Area() << endl;
cout << t1.Area() << endl;
}
At this point, I am feeling a bit lost of the woods and I am sure I have either created several mistakes along the way, or just a few, but regardless, I don't understand. Any advice would be appreciated!
edit: I have updated my code to include the recommendations to include virtual deconstructors, remove the getheight etc... statements, and add virtual to the derived functions
When you're working with inheritance, make sure to use a virtual destructor in all of your inherited classes, as well as the base class.
Your inherited virtual functions would benefit from being marked virtual and override too, in case you want to make further specializations.
You are overriding inherited functions, but then they do the same thing as the original, e.g. GetHeight(). That kinda defeats the point of inheriting those functions. They also do not need to be virtual if they aren't overridden.
Your derived classes would benefit from explicitly calling the base class's constructor. It will call the default constructor if you don't provide a specific constructor to call, which may or may not be the behaviour you intended - IMO it's safer to always provide the base class constructor you want!
As an example:
class Shape {
protected:
float height, width;
public:
Shape() {
height = 0;
width = 0;
}
Shape(float h, float w) {
height = h;
width = w;
}
virtual float Area() const = 0;
virtual float Circumference() const = 0;
virtual ~Shape() {};
};
class Circle: public Shape {
Point center;
float radius;
public:
Circle() : Shape() {};
Circle (Point p1, float r) : Shape() {
// Note you may wish to set the height and width here!
//Takes center point object, and given radius.
center = p1;
radius = r;
}
virtual float Area() const override { // Calculates circle area
return(M_PI * radius * radius);
}
virtual float Circumference() const override { // Calculates circumference
return(float (M_PI * 2 * radius));
}
virtual ~Circle() {};
};
This question already has answers here:
How define an array of function pointers in C
(5 answers)
Closed 4 years ago.
My problem is: I want to write a program which create an array function pointers. I know how to make pointer to function, but don't know how to make array of them.
This is what I tried up to now:
double add(double a, double b) { return a + b; }
double sub(double a, double b) { return a - b; }
double mult(double a, double b) { return a * b; }
double div(double a, double b) { return a/b; }
int main() {
double(*Padd)(double a, double b);
double(*Psub)(double a, double b);
double(*Pmult)(double a, double b);
double(*Pdiv)(double a, double b);
Padd = &add;
Psub = ⊂
Pmult = &mult;
Pdiv = ÷
}
In my code I create these pointers to functions in an array like e.g.
double Tpointers[3];
Tpointers[0] = Padd;
Tpointers[1] = Psub;
Tpointers[2] = Pmult;
Tpointers[3] = Pdiv;
How do I do this?
Simply declare a new type 'Tpointers' that represent a pointer to a function that give two double and return a double.
And in the code you can create an array of functions.
#include<iostream>
// The function pointer type!
typedef double (*Tpointers)(double, double);
double add(double a, double b) { return a + b; }
double sub(double a, double b) { return a - b; }
double mult(double a, double b) { return a * b; }
double div(double a, double b) { return a / b; }
int main() {
// A functions pointers array .
Tpointers fun_array[4];
// Assign the values
fun_array[0] = &add;
fun_array[1] = ⊂
fun_array[2] = &mult;
fun_array[3] = ÷
// A little test
std::cout << fun_array[2](3, 3) << " " << fun_array[3](3,3) << " " << fun_array[1](3,3)
<< std::endl;
return 0;
}
In c++ you can also create an std::vector of functions pointer ... or any containers from the std libraries of "Tpointers".
I am having trouble using a set function in a class file. So far I have the following. I am trying to write a quadratic class that has three private data members and can calculate both the value of a quadratic and the number of real roots in the quadratic. I'm not stuck on the math part as much as I am getting the set methods to not give me weird values. When I test using main, the values for a, b, and c are numbers that I didn't input when I created the object.
Quadratic.hpp
#ifndef QUADRATIC_HPP
#define QUADRATIC_HPP
class Quadratic
{
private:
double a;
double b;
double c;
public:
Quadratic();
Quadratic(double, double, double);
void setA(double);
void setB(double);
void setC(double);
double getA();
double getB();
double getC();
double valueFor(double);
int numRealRoots();
};
#endif
Quadratic.cpp
#include <cmath>
#include <iostream>
Quadratic::Quadratic()
{
setA(1.0);
setB(1.0);
setC(1.0);
}
Quadratic::Quadratic(double A, double B, double C)
{
a = A;
b = B;
c = C;
}
void Quadratic::setA(double A)
{
a = A;
}
void Quadratic::setB(double B)
{
a = B;
}
void Quadratic::setC(double C)
{
c = C;
}
double Quadratic::getA()
{
return a;
}
double Quadratic::getB()
{
return b;
}
double Quadratic::getC()
{
return c;
}
double Quadratic::valueFor(double x)
{
return (a*(pow(x,2)) + b*x + c);
}
int Quadratic:: numRealRoots()
{
double discriminant = pow(b,2) - (4*a*c);
double epsilon = 0.00001;
int realRoots;
if (discriminant <= epsilon && discriminant > 0)
realRoots = 1;
else if (discriminant > epsilon)
realRoots = 2;
else
realRoots = 0;
return realRoots;
}
Your setB method is wrong - it updates a instead of b:
void Quadratic::setB(double B)
{
b = B; // Was "a = B;" in the original code
}
I've been having trouble trying to implement objects from class Cart_Vector in class Cart_Point. My compiler has been listing the following errors and I can't seem to fix them:
friend Cart_Point operator+(const Cart_Point&p1,const Cart_Vector&v1);
'Cart_Vector' does not name a type
Cart_Point operator+(const Cart_Point&p1, const Cart_Vector&v1)
'Cart_Vector' does not have a type
x = p1.x + v1.x; request for member 'x' in 'v1', which is of non-class
type 'const int'
y = p1.y + v1.y; request for member 'y' in 'v1', which is of non-class
type 'const int'
return Cart_Vector(x,y); 'Cart_Vector' was not declared in this scope
#include <iostream>
#include <math.h>
using namespace std;
class Cart_Point
{
public:
double x;
double y;
friend class Cart_Vector;
Cart_Point (double inputx, double inputy);
friend Cart_Point operator<<(const Cart_Point&p1, const Cart_Point&p2);
friend Cart_Point operator+(const Cart_Point&p1,const Cart_Vector&v1);
friend Cart_Point operator-(const Cart_Point&p1,const Cart_Point&p2);
double Cart_distance(Cart_Point, Cart_Point);
};
Cart_Point::Cart_Point(double inputx, double inputy)
{
x = inputx;
y = inputy;
}
double Cart_Point::Cart_distance(Cart_Point p1, Cart_Point p2)
{
double distance = (sqrt( pow(p1.x - p2.x,2) + pow(p1.y - p2.y,2) ));
return distance;
//returns distance between p1 (point 1) and p2 (point 2)
}
Cart_Point operator<<(const Cart_Point&p1, const Cart_Point&p2)
{
cout << "p1:(" << p1.x << ", " << p1.y << ")" << endl;
cout << "p2:(" << p2.x << ", " << p2.y << ")" << endl;
return p1,p2;
//this function should just print each point
}
Cart_Point operator+(const Cart_Point&p1, const Cart_Vector&v1)
{
double x,y;
x = p1.x + v1.x;
y = p1.y + v1.y;
return Cart_Point(x,y);
//this function should make a new Cart_Point
}
Cart_Point operator-(const Cart_Point&p1, const Cart_Point&p2)
{
double x,y;
x = p1.x- p2.x;
y = p1.y - p2.y;
return Cart_Vector(x,y);
//this function should make a new Cart_Vector
}
class Cart_Vector
{
public:
double x; //x displacement of vector
double y; //y displacement of vector
Cart_Vector(double inputx, double inputy);
friend Cart_Vector operator*(const Cart_Vector&v1, double d);
friend Cart_Vector operator/(const Cart_Vector&v1, double d);
Cart_Vector operator<<(const Cart_Vector&v1);
friend class Cart_Point;
};
Cart_Vector::Cart_Vector(double inputx, double inputy)
{
x = inputx;
y = inputy;
}
Cart_Vector operator*(const Cart_Vector&v1, double d)
{
double x,y;
x = v1.x*d;
y = v1.y*d;
return Cart_Vector(x,y);
//this function should make a new Cart_Vector
}
Cart_Vector operator/(const Cart_Vector&v1, double d)
{
double x,y;
if (d == 0)
{
x = v1.x;
y = v1.y;
}
x = v1.x/d;
y = v1.y/d;
return Cart_Vector(x,y);
//this function should make a new Cart_Vector and dividing by zero creates v1
}
Cart_Vector Cart_Vector::operator<<(const Cart_Vector&v1)
{
cout <<"v1: <" << v1.x << ", " << ">" << endl;
return v1;
//this function should just print v1
}
//TestCheckpoint1.cpp file below
int main()
{
//I haven't finished the main function to test all the functions yet
return 0;
}
split your code in different files but your implementation of operator << is wrong , consider following code , its just a hint to help
#include <iostream>
#include <math.h>
using namespace std;
class Cart_Vector
{
public:
double x; //x displacement of vector
double y; //y displacement of vector
Cart_Vector(double inputx, double inputy);
friend Cart_Vector operator*(const Cart_Vector&v1, double d);
friend Cart_Vector operator/(const Cart_Vector&v1, double d);
friend std::ostream& operator<<( std::ostream& out,const Cart_Vector&v1);
friend class Cart_Point;
};
Cart_Vector::Cart_Vector(double inputx, double inputy)
{
x = inputx;
y = inputy;
}
Cart_Vector operator*(const Cart_Vector&v1, double d)
{
double x,y;
x = v1.x*d;
y = v1.y*d;
return Cart_Vector(x,y);
//this function should make a new Cart_Vector
}
Cart_Vector operator/(const Cart_Vector&v1, double d)
{
double x,y;
if (d == 0)
{
x = v1.x;
y = v1.y;
}
x = v1.x/d;
y = v1.y/d;
return Cart_Vector(x,y);
//this function should make a new Cart_Vector and dividing by zero creates v1
}
std::ostream& operator<<(std::ostream &out, const Cart_Vector&v1)
{
out <<"v1: <" << v1.x << ", " << ">" << endl;
return out;
//this function should just print v1
}
class Cart_Point
{
public:
double x;
double y;
friend class Cart_Vector;
Cart_Point (double inputx, double inputy);
friend std::ostream& operator<<(std::ostream& out , const Cart_Point&p2);
friend Cart_Point operator+(const Cart_Point&p1,const Cart_Vector&v1);
friend Cart_Point operator-(const Cart_Point&p1,const Cart_Point&p2);
double Cart_distance(Cart_Point, Cart_Point);
};
Cart_Point::Cart_Point(double inputx, double inputy)
{
x = inputx;
y = inputy;
}
double Cart_Point::Cart_distance(Cart_Point p1, Cart_Point p2)
{
double distance = (sqrt( pow(p1.x - p2.x,2) + pow(p1.y - p2.y,2) ));
return distance;
//returns distance between p1 (point 1) and p2 (point 2)
}
std::ostream& operator<<(std::ostream &out, const Cart_Point&p1)
{
// Since operator<< is a friend of the Cart_Point class, we can access Point's members directly.
out << "p:(" << p1.x << ", " << p1.y << ")" << endl;
return out;
//this function should just print each point
}
Cart_Point operator+(const Cart_Point&p1, const Cart_Vector&v1)
{
double x,y;
x = p1.x + v1.x;
y = p1.y + v1.y;
return Cart_Point(x,y);
//this function should make a new Cart_Point
}
Cart_Point operator-(const Cart_Point&p1, const Cart_Point&p2)
{
double x,y;
x = p1.x- p2.x;
y = p1.y - p2.y;
return Cart_Point(x,y);
//this function should make a new Cart_Vector
}
//TestCheckpoint1.cpp file below
int main()
{
Cart_Point point1(2.0, 3.0);
std::cout << point1;
//I haven't finished the main function to test all the functions yet
return 0;
}
Wandbox :
Do yourself a favor and split your code in different files,at least one .h for Cart_Vector, one .h for Cart_Point, and one .cpp for the test script (main). You can correct this code to make it work (just swap the order of the two classes), if you correct other errors too, like in the overloading of the operator "-".
The point here is that if you start coding in this way, when you start programming complex projects you will find yourself in great difficulties. Coding one public (non-inner) class-per file is like applying Single Responsibility Principle for files too. I would say that also a file should have only one reason to change, and this has great benefits in readability and when will you perform version control.
Cart_Vector and Cart_point need each other. So you need to implement these classes in separate header files. Do not forget include them. Also in here ;
Cart_Point operator-(const Cart_Point&p1, const Cart_Point&p2)
{
double x,y;
x = p1.x- p2.x;
y = p1.y - p2.y;
//return Cart_Vector(x,y);
return Cart_Pointer(x,y);
//this function should make a new Cart_Vector
}
You can not access non-const elements of const object and you can not call non-const functions. You can pass these objects by value if you want it.