String toInt() by Tom Igoe

Reads a serial input string until it sees a newline, then converts the string to a number if the characters are digits.

String inString = "";    // string to hold input

void setup()
{
  // Initialize serial communications:
  Serial.begin(9600);
}

void loop()
{
  // Read serial input:
  while (Serial.available() > 0)
  {
    int inChar = Serial.read();
    if (isDigit(inChar))
    {
      // convert the incoming byte to a char
      // and add it to the string:
      inString += (char)inChar;
    }
    // if you get a newline, print the string,
    // then the string's value:
    if (inChar == '\n')
    {
      Serial.print("Value:");
      Serial.println(inString.toInt());
      Serial.print("String: ");
      Serial.println(inString);
      // clear the string for new input:
      inString = "";
    }
  }
}