Difference between various initializers in C++

Question

I've only recently started learning C++ as part of my 10th Grade syllabus, and am only aware of the basics, thus simple answers (if possible) will be appreciated. I'm rather confused between initialization and assignment.

//Case 1
int a=5; //This is initialization
a=6; //This is assignment

From what I've understood, a variable is initialized when you give it a value to hold while declaring it. Changing this later in the code will be an assignment. Right?

What about :

//Case 2
int b;
{
//Block of code which does not call variable b
.
.
.
//End of block
}
b=6; // Is this initialization as well?

While 'b' is uninitialized when we declare, we later assign the value '6'. Can we say the 'b' is initialized now? Or are the terms initialized and uninitialized not applicable to 'b' anymore?

I read the an uninitialized variable holds "garbage values" till it isn't initialized. What exactly are "garbage values"?

What is the difference between the following initializers : '()', '{}', and '='?

Answer 1

Okay, once you declare a variable without assigning any value, like

int b; 

that means that the compiler reserves some space in the memory to hold the value (to be exact, in this case the memory is reserved on the stack). But since you didn't assign any value to the variable, it still holds the value, that the assigned space in memory had before. And that can be anything. Those are garbage values.

Initializers:

int b(1);

assigns the value 1 to be (in general, it calls a constructor of the type)

The brackets can be used to initialize arrays like this (edit):

int b[] = {1, 3, 5, 7};

And the = just assigns a value. The difference between this and the first will only become interesting when dealing with more complex types (classes), where you have constructors

Answer 2

Easilly spoken:

Uninitialize variable:

 int a;

You are declare a variable that means you allocate memory but dont assign a value to it. So its compiler dependend if the value is set to 0 or not. So there could be anything in. Thats waht you called garbage values.

Initialized variable:

int a = 0;

You are declare a variable that means you allocate memory and assigne a value to it.

Assigne Values:

a = 10;

You assigne a rvalue (in this case 10) to a lvalue ( a). So you dont allocate new memory.