Reference →

isLowerCase()

Analyse if a char is lower case (that is a letter in lower case). Returns true if thisChar contains a letter in lower case. isLowerCase(thisChar)
 thisChar: variable. Allowed data types: char. true: if thisChar is lower case. 
		
if (isLowerCase(myChar)) {  // tests if myChar is a lower case letter
  Serial.println("The character is lower case");
}
else {
  Serial.println("The character is not lower case");
}