In your question there are following operator are used..
Post increment operator:-. eg...a++ (aplusplus)that means it first use the value then after increase it by 1and use it..so a=5
So,*******""first output is 5
Pre increment operator:- eg.++a (plusplus a) that means it first increase the value by 1 and after then use..above a store the value 6 then
So,******""second output is 7
Pre decrement operator:- eg.--a(minus minus a) that means it first decrease the value by 1 and after then use.above a store 7
Then
So,******""Third output is 6