While passwords generally have few restrictions, they are normally not totally f
ID: 3793773 • Letter: W
Question
While passwords generally have few restrictions, they are normally not totally free. Suppose that in a certain system passwords can be of arbitrary length, but must contain at least one letter, a...z and one number 0...9. Construct a grammar that generates the set of such legal passwords. Suppose that in some programming language numbers are restricted as follows: (a) a number may be signed or unsigned. (b) the value field consists of two nonempty parts, separated by a decimal point. (c) there is an optional exponent field. If present this field must contain the letter e, followed by a signed two-digit integer.Design a grammar for the such numbers. Suppose that a certain programming language permits only identifiers that begin with a letter, contain at least one but no more than three digits, and can have any number of letters. Give a grammar and an accepter for such a set of identifiers.Explanation / Answer
PART 1:
GRAMMAR GENERATING THE SET OF LEGAL PASSWORDS CONTAINING AT LEAST ONE LETTER FROM a TO z AND ONE NUMBER FROM 0 TO 9 AND OF ARBITRARY LENGTH:
S -> S1CS2 | S2CS1
C -> S1CS2 | S2CS1 | CS1C | CS2C | CC |
S1 -> a|b|……… |z
S2 -> 0|1| …… |9
PART 2:
GRAMMAR GENERATING THE GIVEN TYPE OF NUMBERS:
S -> S1N1.N1S2
S1 -> + | -
S2 -> e N1C N1 |
N1 -> N1C N1 | 0 | 1 | … |9
C -> N1C N1 |
S -> S1CS2 | S2CS1
C -> S1CS2 | S2CS1 | CS1C | CS2C | CC |
S1 -> a|b|……… |z
S2 -> 0|1| …… |9
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