String length() by Tom Igoe

Examples of how to use length() in a String. Open the Serial Monitor and start sending characters to see the results.

String txtMsg = "";                         // a string for incoming text
int lastStringLength = txtMsg.length();     // previous length of the String

void setup()
{
  // open the serial port:
  Serial.begin(9600);
}

void loop()
{
  // add any incoming characters to the String:
  while (Serial.available() > 0)
  {
    char inChar = Serial.read();
    txtMsg += inChar;
  }

  // print the message and a notice if it's changed:
  if (txtMsg.length() != lastStringLength)
  {
    Serial.println(txtMsg);
    Serial.println(txtMsg.length());
    // if the String's longer than 140 characters, complain:
    if (txtMsg.length() < 140)
    {
      Serial.println("That's a perfectly acceptable text message");
    }
    else
    {
      Serial.println("That's too long for a text message.");
    }
    // note the length for next time through the loop:
    lastStringLength = txtMsg.length();
  }
}