what does if (!flag) means ??

Answer 1

flag , - + # 0. all are ..

Answer 2

if(!flag) means that if flag is not equal to 0......so if flag!=0 then the if block will be executed otherwise the corresponding else block will be executed.

Answer 3

flag is a boolean and is probably set in the previous lines of the code. if(!flag) is the same as if(flag==false)