does not behave as I expect

In my program I have these codelines

Serial.println(F("Simple Termometer\n\r"));;

The first string is printed correctly. But then instead of waiting for character from the terminal window (as I would expect) it keeps printing a garbage token. Why ? How do I get the program to wait and read a character when I send it from the terminal ?

Your expectation of how works is not aligned with reality.
If there is nothing to read, it returns -1, your garbage token.

If you want to wait, use Serial.available()

We were actually just talking about this in this thread:;topicseen#new

Although this may not be the best way to do things it should work and maybe get you moving along.