Reqular Expressions Questions

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101.

Which of the following is correct?
Statement 1: ? represents a single string in the set.
Statement 2: ? represents the language that consist of no string.

A

Statement 1 and 2 both are correct

B

Statement 1 is false but 2 is correct

C

Statement 1 and 2 both are false

D

There is no difference between both the statements, ? and ? are different notation for same reason

Correct Answer: A

? represents a single string in the set namely, the empty string while Statement 2 is also correct.

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102.

The appropriate precedence order of operations over a Regular Language is

A

Kleene, Union, Concatenate

B

Kleene, Star, Union

C

Kleene, Dot, Union

D

Star, Union, Dot

Correct Answer: C

If a regular language expression is given, the appropriate order of precedence if the parenthesis is ignored is: Star or Kleene, Dot or Concatenation, Union or Plus.

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103.

Regular Expression R and the language it describes can be represented as:

A

R, R(L)

B

L(R), R(L)

C

R, L(R)

D

All of the mentioned

Correct Answer: C

When we wish to distinguish between a regular expression R and the language it represents; we write L(R) to be the language of R.

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104.

Let for ?= {0,1} R= (???) *, the language of R would be

A

{w | w is a string of odd length}

B

{w | w is a string of length multiple of 3}

C

{w | w is a string of length 3}

D

All of the mentioned

Correct Answer: B

This regular expression can be used to eliminate the answers and get the result. The length can be even and as well more than 3 when R= (???) (???) (particular case).

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105.

If ?= {0,1}, then ?* will result to:

A

?

B

?

C

?

D

None of the mentioned

Correct Answer: A

The star operation brings together any number of strings from the language to get a string in the result. If the language is empty, the star operation can put together 0 strings, resulting only the empty string.

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106.

The given NFA represents which of the following NFA

A

(ab U a) *

B

(a*b* U a*)

C

(ab U a*)

D

(ab)* U a*

Correct Answer: A

The Regular expression (ab U a) * is converted to NFA in a sequence of stages as it can be clearly seen in the diagram. This NFA consist of 8 stated while its minimized form only contains 2 states.

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107.

Which of the following represents a language which has no pair of consecutive 1

A

(0+10)*(1+?)

B

(0+10)*(1+?)*

C

(0+101)*(0+?)

D

(1+010)*(1+?)

Correct Answer: A

All the options except

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108.

The finite automata accept the following languages:

A

Context Free Languages

B

Context Sensitive Languages

C

Regular Languages

D

All the mentioned

Correct Answer: C

A finite automaton accepts the languages which are regular and for which a DFA can be constructed.

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109.

(a + b*c) most correctly represents:

A

(a +b) *c

B

(a)+((b)*.c)

C

(a + (b*)).c

D

a+ ((b*).c)

Correct Answer: D

Following the rules of precedence, Kleene or star operation would be done first, then concatenation and finally union or plus operation.

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110.

Which of the following regular expressions represents the set of strings which do not contain a substring

A

(rt)*

B

(tr)*

C

(r*t*)

D

(t*r*)

Correct Answer: D

As Kleene operation is not on the whole of the substring, it will not repeat and maintain the order of t, r.

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