Why this is happening

Question

class A{int a;}
main(){
A b=new A();
b.a++;
}
//no errors

but when I do that
main(){
int x;
x++;
//error
}

maybe because of the type of variable
the first is global and the second is local

Answer 1

In the second one you haven't initialized the local variable, so you can't do any operations on it.

In the first one, class level variables are initialized to their default values when you create a new object, so the int in the class A initializes to 0

Answer 2

Please refer:
https://www.sololearn.com/Discuss/1493224/?ref=app