Why Does C# Allow Variable Scope to Extend Throughout a Block Regardless of Declaration Order? (Book Reference: C#10 in a Nutshell by Joseph Albahari)

I am reading a book titled C#10 in a Nutshell by Joseph Albahari OReilly. When describing local variables, the book says the following:

int x; 

{ 
    int y; 
    int x; // Error - x already defined 
} 

{ 
    int y; // OK - y not in scope 
} 

Console.Write (y); // Error - y is out of scope 

"A variable’s scope extends in both directions throughout its code block. This means that if we moved the initial declaration of x in this example to the bottom of the method, we’d get the same error. This is in contrast to C++ and is somewhat peculiar, given that it’s not legal to refer to a variable or constant before it’s declared." – Chapter 2 of C#10 in a Nutshell

I have tried ChatGPTing this and looking for an explanation online but haven’t found a clarification yet. Could someone please explain what this means? Any insights on this scope behavior and its implications would be appreciated!

>Solution :

A { } pair encloses a new "scope", a block where a certain variable is valid.

Both y‘s are declared in sibling scopes. They will not interfere with each other. Also they will not be available in a parent scope – that’s why the Console.WriteLine fails.

However, one x is defined in the "parent" scope and another in a child scope. This child declaration clashes with the one declared in the parent scope. And this would even be the case when you move the "parent" int x to the end of the block, even though it is then not valid to use it earlier.

{
    int x; // Error - x already defined 
}

int x;