I read from serial and don't work correctly, if i use the interface of arduino yes but when i write from the pc don't.
I think the char I read is codific in UTF-8, how I can convert to Ascii string for a correct work?
If you are using the serial monitor to send data to the Arduino, the data is sent in ASCII as a series of characters.
When you read those characters, and store them in an array, as you are doing, you are NOT creating a string that can be passed to strcmp.
If, after adding the character read from the serial port to the array, you added a NULL terminator in the next position, you WOULD be creating a string that can be passed to the strcmp function.