# Finite Automata in Real-life Situations

Learn about some real-life applications of finite automata.

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The concepts of a start state, accepting state, and changing state depending on input stimuli can also be found in many real-life scenarios: scoring a tennis game, modeling a vending machine, or opening and closing an automatic door. All of them can be depicted using “state machines” as discussed below.

## Scoring a tennis game

The machine in the figure below illustrates how to score a tennis game. Each time a player wins a volley, the score progresses through the following point-level sequence: love (0), 15, 30, 40, game. When the score is tied 40–40, it is called a **deuce**. To win the game from deuce, a player must win two volleys in a row. Winning the first volley from the deuce gives the player the “advantage,” but that player must win the very next volley to win the game. Otherwise, the play returns to deuce. This could go on for some time. Observe the cycles between the *Deuce* state and the advantage states *Ad-S* and *Ad-O* in the figure below.

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