Newb requests help with basic syntax

Hi all.

This is my first attempt a OO in C++. I'm sure there are some obvious mistakes. I know there must be more than one way to do this, but I would like to follow a partial example I was given and leave the first 15 lines unchanged (if possible) and continue using stdio.h too.

I might respond with slightly different approaches for critiquing in the thread too; the key point is I'm just trying to learn.

Code:

---

#include <stdio.h>
#include <stdlib.h>

class SomeClass{
        private:
                int x;
                int y;
                int z;
               
        public:
                SomeClass(int x, int y, int z){
                        this->x = x;
                        this->y = y;
                        this->z = z;
                }
               
        void print(SomeClass z){
                print("%d %d %d\n", z.x, z.y, z.z);
        }
};
               
        int main(){

                SomeClass a (1, 2, 3);
                SomeClass b (4, 5, 6);
       
                print(a);
                print(b);
       
                return 0;
}

---

Thanks in advance.

- private is implicit
- don't need return 0
- print text should be printf, or use c++ cout
- print doesn't need arguments if its inside the class, if its outside u need to "friend" it
- indentation should line up

Code:

---

#include <stdio.h>
#include <stdlib.h>

class SomeClass
{
    int x;
    int y;
    int z;

    public:
        SomeClass(int x, int y, int z)
        {
            this->x = x;
            this->y = y;
            this->z = z;
        }

        void print()
        {
            printf("%d %d %d\n", x, y, z);
        }
};


int main()
{
    SomeClass a(1, 2, 3);
    SomeClass b(4, 5, 6);

    a.print();
    b.print();
}

---

Is it not necessary to always return 0 when main() is of type int?

I thought it was always good to return 0 to signify that main() had executed successfully.

Quote:

---

Originally Posted by Swerve

Is it not necessary to always return 0 when main() is of type int?

---

The return type of the global main function must be int, but explicitly returning 0 from it is optional.

Thank you Dae!

Now, I have a follow up question if anyone can help...

I would like to write a 'global function' that is *outside* of the class. This function should be able to work with two different objects. Here's what I tried (it does not compile):

Code:

---

#include <stdio.h>
#include <stdlib.h>

int someGlobalFunction(SomeClass x, SomeClass y);

class SomeClass{
    private:
                int x;
                int y;
                int z;

    public:
        SomeClass(int x, int y, int z)
        {
            this->x = x;
            this->y = y;
            this->z = z;
        }

        void print()
        {
            printf("%d %d %d\n", x, y, z);
        }
};


int main(){
    SomeClass a(1, 2, 3);
    SomeClass b(4, 5, 6);

    a.print();
    b.print();
}

int someGlobalFunction(SomeClass a, SomeClass b){
                return a.getX() + b.getY + b.getZ();
}

SomeClass::getX(){return x}
SomeClass::getY(){return y}
SomeClass::getZ(){return z}

---

Quote:

---

Originally Posted by Roger

I would like to write a 'global function' that is *outside* of the class. This function should be able to work with two different objects. Here's what I tried (it does not compile):

---

The problem is that you declared the function with SomeClass parameters, but SomeClass has not yet been declared. You could fix this with a forward declaration:

Code:

---

class SomeClass;

int someGlobalFunction(SomeClass x, SomeClass y);

---

or you could simply declare someGlobalFunction after defining SomeClass, since a class definition is also a class declaration.

Given what you appear to be doing, this is one way of doing it:

Code:

---

#include <cstdio>

class SomeClass {
public:
    SomeClass(int x, int y, int z) : x(x), y(y), z(z) {}

    int getX() const;
    int getY() const;
    int getZ() const;
private:
    int x;
    int y;
    int z;
};

void print(const SomeClass& obj);
int someGlobalFunction(const SomeClass& x, const SomeClass& y);

int main() {
    SomeClass a(1, 2, 3);
    SomeClass b(4, 5, 6);

    print(a);
    print(b);
}

void print(const SomeClass& obj)
{
    std::printf("%d %d %d\n", obj.getX(), obj.getY(), obj.getZ());
}

int someGlobalFunction(const SomeClass& a, const SomeClass& b) {
    return a.getX() + b.getY + b.getZ();
}

// ...

---

Notice that I have:

• Included <cstdio> instead of <stdio.h>
• Used a constructor initialisation list instead of assigning in the constructor body.
• Declared the public members of the class before the private members.
• Added in the missing declarations for getX() etc.
• Changed print to be a free function since it can use the getter functions.
• Pass SomeClass by const reference instead of by value since you do not actually need to copy.
• Shifted the declaration of someGlobalFunction to after the class definition.

My indentation is more consistent than yours too :)
You should add in the getter function definitions and fix the compile errors that result.

b.getY should be b.getY().