There are many basic things that I do not know, for example how to read exactly this exclamation in the following way:
if (!(periodoAnterior.Equals(dataReader["NOMEPERIODO"].ToString()))){
//...
}
Can anyone explain me? And taking advantage, does this Equals do the same as "=="?
Anything you put inside a if(aqui) will be transformed into true or false . The body of if only executes if the result is true .
Let's simplify your example by saving the result of Equals to a variable:
bool resultado = periodoAnterior.Equals(dataReader["NOMEPERIODO"].ToString());
The variable resultado contains true or false . So we have two options for if :
if (!(true)) {}
if (!(false)) {}
What the exclamation ! does is to invert the value of a boolean: !true (reads "not true") is false , and !false is true . Therefore, the possible results for if will be:
if(false) {} // aqui o corpo nunca executa
if(true) {} // aqui o corpo executa
So, in your code, the body of if only executes if the result of periodoAnterior.Equals(dataReader["NOMEPERIODO"].ToString()) is false .
Note: Your doubt about Equals deserves a separate question, but probably who wrote that led to C # a Java addiction. More details and exceptions on link
! is the negation operator. It returns the opposite of the resolution of the operation it precedes.
That is:
!true == false
!false == true
!(2 == 2) == false
!(2 == 1) == true