How to subtract a value from a struct?

Question

I have this code currently

struct monster {
short health, attack;
monster() : health{50}, attack{10} { }
};

How would I go about subtracting for sample 20 health so that the health becomes 30?

Answer 1

FIRST CREATE VARIABLE OF TYPE monster SUPPOSE M1.

THAN

M1.health - 20

Answer 2

monster M1;

Answer 3

how would i create the variable