quick syntax question

hi,

I have this piece of code from a course I'm studying, but I can't make out all the details. Could someone please explain some of the syntax to me?

Code:

class A {
 public:
  A();
  A(int i);
  void setVarA (int i);
  int getVarA ();
 private:
  int varA; 
};

class B : public A {
 public:
  B();
  B(int i);
  B(int vara, int varb);	
  void setVarB (int i);
  int getVarB ();
 private:
  int varB;
};

A::A():varA(0) {}
A::A(int i):varA(i) {}
B::B():A(),varB(0) {}
B::B(int i):A(),varB(i) {}
B(int vara, int varb):A(vara), varB(varb){}

I know about classes, about namespaces and inheritance. So I get the decleration of the classes A & B, with their constructors, methods etc.
What I don't get is the last bit of code:

Code:

A::A():varA(0) {}
A::A(int i):varA(i) {}
B::B():A(),varB(0) {}
B::B(int i):A(),varB(i) {}
B(int vara, int varb):A(vara), varB(varb){}

I know A::A() calls A's constructor, but what does the added :varA(0) do? is it a way to define the constructors outside the class? If so, can it be done to other functions as well?
I'd very much appreciate if someone could put a name to this technique so I can do some reading on it.

thx in advance

Those are initialization lists: Initialization Lists in C++ - Cprogramming.com

thx!