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char myChar = ' '; // try with 'A' for a printable char

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

  if (isGraph(myChar)) {  // tests if myChar is a printable character but not a blank space.
    Serial.println("The character is printable");
  }
  else {
    Serial.println("The character is not printable");
  }
}

void loop() {
}