1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

char myChar = 'A'; // try with '#' for a non alpha char

void setup() {
  Serial.begin(9600);

  if (isAlpha(myChar)) {  // tests if myChar is a letter
    Serial.println("The character is a letter");
  } else {
    Serial.println("The character is not a letter");
  }
}

void loop() {
}