ISRO2011-43

Question

Which variable does not drive a terminal string in grammar?

• $S \rightarrow AB$
• $A \rightarrow a$
• $B \rightarrow b$
• $B \rightarrow C$

• A. A
• B. B
• C. C
• D. S

Comments

Options for this question are:

a . A

b. B

c. C

d. S

Answer 1

Here

S -> AB

{A ->a} and {B ->b or C}

if B goes with C then, there is no termination string.

So, answer is 'C' . which is also called useless symbol.

Comments

c or d?

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yes.  C is useless symbol.

So, option D where B is deriving an un-terminated symbol.

ie. B -> C.

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Options for this question are:

a . A

b. B

c. C

d. S

Answer 2

C is the variable which do not derive any terminal, its also called useless symbol,

after reducing useless variables your remaining grammar is,

S--> AB,  A-->a , B-->b

also see this

Comments

why you deleted production B->b here?

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you are right, i corrected it

Answer 3

its simple as C is unreachable it cannot derive any string