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This example is for Wiring version 1.0 build 0100+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

Comparing Strings by Tom Igoe
Examples of how to compare strings using the comparison operators

    String stringOne, stringTwo;

    void setup()
    {
      pinMode(WLED, OUTPUT);
      digitalWrite(WLED, HIGH);
      Serial.begin(9600);
      stringOne = String("this");
      stringTwo = String("that");
      Serial.println("\n\nComparing Strings:");
    }

    void loop()
    {
      // two strings equal:
      if (stringOne == "this")
      {
        Serial.println("StringOne == \"this\"");
      }
      // two strings not equal:
      if (stringOne != stringTwo)
      {
        Serial.println(stringOne + " =! " + stringTwo);
      }

      // two strings not equal (case sensitivity matters):
      stringOne = "This";
      stringTwo = "this";
      if (stringOne != stringTwo)
      {
        Serial.println(stringOne + " =! " + stringTwo);
      }

      // you can also use equals() to see if two strings are the same:
      if (stringOne.equals(stringTwo))
      {
        Serial.println(stringOne + " equals " + stringTwo);
      }
      else
      {
        Serial.println(stringOne + " does not equal " + stringTwo);
      }

      // or perhaps you want to ignore case:
      if (stringOne.equalsIgnoreCase(stringTwo))
      {
        Serial.println(stringOne + " equals (ignoring case) " + stringTwo);
      }
      else
      {
        Serial.println(stringOne + " does not equal (ignoring case) " + stringTwo);
      }

      // a numeric string compared to the number it represents:
      stringOne = "1";
      int numberOne = 1;
      if (stringOne == (String) numberOne)
      {
        Serial.println(stringOne + " = " + numberOne);
      }

      // two numeric strings compared:
      stringOne = "2";
      stringTwo = "1";
      if (stringOne >= stringTwo)
      {
        Serial.println(stringOne + " >= " + stringTwo);
      }

      // comparison operators can be used to compare strings for alphabetic sorting too:
      stringOne = String("Brown");
      if (stringOne < "Charles")
      {
        Serial.println(stringOne + " < Charles");
      }

      if (stringOne > "Adams")
      {
        Serial.println(stringOne + " > Adams");
      }

      if (stringOne <= "Browne")
      {
        Serial.println(stringOne + " <= Browne");
      }

      if (stringOne >= "Brow")
      {
        Serial.println(stringOne + " >= Brow");
      }

      // the compareTo() operator also allows you to compare strings
      // it evaluates on the first character that's different.
      // if the first character of the string you're comparing to
      // comes first in alphanumeric order, then compareTo() is greater than 0:
      stringOne = "Cucumber";
      stringTwo = "Cucuracha";
      if (stringOne.compareTo(stringTwo) < 0)
      {
        Serial.println(stringOne + " comes before " + stringTwo);
      }
      else
      {
        Serial.println(stringOne + " comes after " + stringTwo);
      }

      delay(10000);  // because the next part is a loop:

      // compareTo() is handy when you've got strings with numbers in them too:

      while (true)
      {
        stringOne = "Sensor: ";
        stringTwo = "Sensor: ";

        stringOne += analogRead(A0);
        stringTwo += analogRead(A5);

        if (stringOne.compareTo(stringTwo) < 0)
        {
          Serial.println(stringOne + " comes before " + stringTwo);
        }
        else
        {
          Serial.println(stringOne + " comes after " + stringTwo);
        }
      }
    }