Question about concept of class

I spent quite a lot of time to try to understand class but still not clear about the concept. Help me please.
1. I saw something like this:

Code:

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bool class::mem_f(int x)
{
    if (!(x%5))// means if x is not divisable by 5
    return true;
}

---

Can the condition be written as : if (x%5!=0) ?If the answer is 'no', why?
2. When & why overload operators?
3. I am not sure about when to use call by reference in arguments of member functions.
When to use call by reference in class? Why use call by reference when overloading operators?Plz explain in simple English.

1) No. x%5 is equivalent to x%5 != 0, therefore !(x%5) is equivalent to x%5 == 0. (The coment above the if gets it the wrong way round. As Mario says below me, doing the explicit one is probably clearer.)

2) You overload operators when doing so makes using your class more intuitive. It takes experience to know when that is.

3) You use call-by-ref-to-non-const whenever you wish to modify the argument.
You use call-by-ref-to-const whenever passing the argument by value, i.e. copying it, would be expensive, or when the object cannot be copied.

None of these questions had anything to do with the concept of a class.

> Can the condition be written as : if (x%5!=0) ?If the answer is 'no', why?

EDIT: I was wrong on this one. Check CornedBee's reply

> When & why overload operators?

I think the short answer fot this is never unless there is a reason. :)
Check http://www.parashift.com/c++-faq-lit...erloading.html

> 3. I am not sure about when to use call by reference in arguments of member functions.

Of the top of my head, on three instances:

- When the argument type doesn't allow for copy operations (a pass by value forces the creation of a new variable and the copying of the argument value into the new variable)

- When you want to avoid the cost of creating a new variable (particularly meaningful when working with large objects)

- When you wish to alter the object from inside the function and retain the new value when you exit the function.

Thank you for your detailed answers. At least I am more clear about when to use call by reference in class. It takes some time for me to digest. Thank you.

a class is the shape of a cookie cutter, and the little cookies you eat look the way they do because the cookie cutter class made them.

simple concept.

http://www.cprogramming.com/tutorial/lesson12.html

Code:

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a class is the shape of a cookie cutter, and the little cookies you eat look the way they do because the cookie cutter class made them.

simple concept.

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It would be totally fun to be a teacher, and explain all the concepts of object oriented programming with that cookie analogy. Ya know, sprinkles -- polymorphism, it's a simple concept. It would also be really fun to lock a baby in a basement and have it only hear beeps. It would totally learn how to express itself in beeps.