C++ class: to static or not

[neelsmail]

Hi,

While adding a class, I usually have question: to make it static or
not. Here is an example:

class myclass {
SomeType someTypeMember;
public:
SomeOtherType DoSomething() const {
//do something with someTypeMember and return SomeOtherType
return someOtherType;
}
};

The same class can be written as (the method I don't prefer):

class myclass {
public:
static SomeOtherType DoSomething(SomeType someTypeVar) {
//do something with someTypeVar and return SomeOtherType
return someOtherType;
}
};

Is there a recommended reason why one style should be preferred than
other?

Thanks in advance,
-Neel.