Assigning a variable within a class with value of a method - c++

Question

Is there a way to assign a variable within a class with a value of a class method?
I was trying the example below, but it is obviously not working. Is there a correct way of doing this?
#include <iostream>
using namespace :: std;
class rectangle
{
public:
rectangle(double h, double w) {
height = h;
width = w;
};
double area(void) {
return height*width;
};
double myarea = (*this).area();
private:
double height, width;
};
int main(void) {
rectangle r(2.5, 3);
cout << "Area is: " << r.area() << endl;
cout << "Area is: " << r.myarea << endl;
return 0;
}
result
Area is: 7.5
Area is: 0

Answer 1

The problem is that member variables are initialized in the order they are declared within the class. Also, your constructor creates the object before you have actually initialized width and height, as you do your initial assignment in the body of the constructor, rather than in an initializer list. Thus, when myarea is initialized (in your code), width and height have not yet been set.
To fix this, you can re-order the members and move the initialization of width and height into a list:
class rectangle {
private:
double height, width; // These will NOW be set before "myarea" is calculated
public:
rectangle(double h, double w) : height{ h }, width{ w } {
// Any assignments done here will be AFTER initialization of "myarea"
}
double area(void) {
return height * width;
}
double myarea = area();
};
Also, you don't need the complex (*this).area() syntax - just area() will do.
EDIT: Another thing to remember is that the setting of myarea by calling the area() function will only be done once (at object creation); if you change either width or height later, you won't (automatically) change myarea.