I think there are low voltage across the pins,so MD1A MD2A MD3A MD4A will not work.
No he was talking about the syntax of that expression.
D1A && MD2A ==LOW
I will tell you what this does not do. It does not set D1A and MD2A equal to low.
To be frank my knowledge of C is not enough to tell you how the compiler will react to it, and I suspect that your knowledge of C is even less than mine. Those lines while they might compile will not do anything useful.
Now what do you actually want to do.
The way this forum works is you get advise, revise your code and post it again ( not modify your original post ) so we can see if you understood the advice.