Instantiating new object within switch block - why does it fail?

switch ([document currentTool]) {
	case DrawLine:
		NSBezierPath * testPath = [[NSBezierPath alloc]init];
        //...rest of code that uses testPath....

switch( ... ) {
    case A:
       MyClass obj( constructor stuff );
       // more stuff
       // fall through to next case
    case B:
       // what is the value of obj here? The constructor was never called
    ...
}

switch( ... ) {
    case A: {
       MyClass obj( constructor stuff );
       // more stuff
       // fall through to next case
    }
    case B:
       // obj does not exist here
    ...
}