Why is this declared void?

[jsk15]

Hi guys.

I'm going through the (really good) tutorials on here and a bit confused at one point. Mainly, in the class CRectangle, why is set_values declared void?

I've commented the program as far as I understand it - feel free to correct me to improve my understanding.

Many thanks
JS

// classes example
#include <iostream>
using namespace std;

class CRectangle {                  // new class called CRectangle
      int x, y;                     // private member variables, x and y
      public:                                  //public member variables
             void set_values (int,int);        //void ??
             int area() {return (x*y);}        //int area returns value x*y ??
};

void CRectangle::set_values (int a, int b) {   //the set_values member is defined outside the class
     x=a;                   //as x=a
     y=b;                   //and b=y
}

int main()
{
    CRectangle rect;                 //declare new object from class CRectangle
    rect.set_values (3,4);           //set_values member is declared here
    cout << "area: " << rect.area(); //public member variable area is output here.
    return 0;
  
}

[kbw]

... because it doesn't return a value. It changes the state of CRectangle.

[lnk2019]

kbw wrote:

because it doesn't return a value

As kbw said, the return type is void as it does not return anything.

The variable type that precedes a function/method prototype defines the type of variable/object that will be returned by it.

You can find documentation about this here: http://www.cplusplus.com/doc/tutorial/functions/ .

There is a nice section at the bottom of the above link that deals with your query.

I hope this helps.

[ascii]

This is somewhat of a stupid example isn't it? set_values is doing what a constructor should do, so why didn't they make a constructor instead?

[kbw]

This is somewhat of a stupid example isn't it?

You're calling tutorial code stupid?

[Albatross]

ascii, unless you intend to create a new object every time you want to change its value, there is some value to that function.

-Albatross

[ascii]

Well yes, but there's only one object here. I do see your point that it could be useful in a longer program however :)

And while the person who wrote the tutorial on this website is certainly a far better C++ programmer than me, yes I am saying that in this example I think a constructor would have been the better way to go. But I'm also unaware of the context (e.g. if the writer wanted to introduce constructors later).

[kbw]

The point is that the program is there to illustrate something. The existence of this thread is testimony to the usefulness of that. I really don't think it's stupid.