New to C# and trying to use a global variable

should help you out Try to learn a PHP framework. They solve these problems better and in an OOP way.
Anyway, in your example, you can remove a lot of the code:

$debug_mode = TRUE;

function dump() {
  global $debug_mode;

  if ($debug_mode) {
    call_user_func_array('var_dump', func_get_args());
  }
}

will be helpful for those in need I found an unexpected 'invalid' C code snippet, which I believed a valid one: ,
Which part of C specification makes this erroneous?

char *pstr = str;

To fix the issue you can do Only assignmemnt is an instruction and each instruction should appear inside a function body.
In global scope only a special case, initialization through assignment while definition is allowed.

I wish this help you So this is basically how the code works that I'm using. , The problem here is the following line:

Lvar = Gvar

Lvar = Gvar[:]

global Gvar
Gvar = ["Hello"]

def someFunction():
    Lvar = Gvar[:]
    Lvar.append("World")
    print(Lvar)
    print(Gvar)

someFunction()

it helps some times In your code, the constant GET_CART_ALL_ITEM is created and initialize only one time, and it takes the current value of ReturnUserRrQuote(). Later It will not trigger the function as the constant already has its value and does not require a new initialization.
If at the beginning of code ReturnUserRrQuote() => "100". Then GET_CART_ALL_ITEM is created and initialize with this value, it will be "store/3/cart/100/type/customer" and not "store/3/cart/" + ReturnUserRrQuote() + "/type/customer". It's due cause at initialization the expression "store/3/cart/" + ReturnUserRrQuote() + "/type/customer" is evaluated and the result is affected to the constant (the expression is not affected to the constant).

public static final const1 = "store/3/cart/";
public static final const2 = "/type/customer";

//whenever you have to obtain your value
String value = const1 + ReturnUserRrQuote() + const2;

//Static function that return the number of times it has been called
public static returnNumber() {
    final int i=1;
    return i++;
 }

public static void main() {
    int a = returnNumber(); //Initialize a
    for (j=0; j<10; j++) {
        System.out.println(a); //print the current value of a
    }
}