if i do this :
chaine=String(adresse)+" "+String(Valeur)+" a="+String(a)+" b="+String(b)+" c="+String(c);
Serial.println(chaine);
then bug
What kind of bug? Converting each value to a separate String is completely unnecessary.
In this snippet you have 5 calls to the String constructor (requiring 5 calls to the matching destructor) as well as 8 calls to the concatenation operator. For what? The device on the other end of the serial port won't be able to tell the difference between the output generated by this snippet and the other one that doesn't waste resources using the String class.