String

A string is a finite sequence of symbols of a given alphabet.

• Let $\sum =\{A,B,C,\dots ,Z\}$
  • So “PASSWORD” is a valid string.
  • but “PASSWORD1” is not a valid string.
• Let $\sum =\{0,1\}$
  • “0” is a valid string.
  • “000000000000000000” is a valid string.
  • “000000…000000” infinite times is not a valid string (not finite)