basic question about adresses and values in structs

[nikki via Digitalmars-d-learn]

so I am still very new to structs and & and * adress and pointer 
stuff, I have this basic code :

    struct S {
        int value = 0;
    }
    void func(S thing){
        writeln(&thing); //BFC52B44
        thing.value = 100;
    }

    S guy = {value:200};
    writeln(&guy); //BFC52CCC
    func(guy);
    writeln(guy.value);// this prints 200, because the adress was 
not the same

I think I see whats going on but I don't know how to fix it?