Regular Expressions MCQs | Compiler Design

MCQ

31.

Let L1 = {w ? {0,1}? | w has at least as many occurrences
of (110)



                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    L1 is regular but not L2                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    L2 is regular                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    L1 and L2 are regular                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    Neither of them are regular                                                
                                            
                                                                                                            

                                
                                    Correct Answer: A
                                    L1 is regular but not L2



                        
                            

                            
                            
                                                        
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                                    32.
                                    The length of the shortest string NOT in the language (over ? = {a, b}) of the following regular expression is _____________
a*b*(ba)*a*
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    2                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    3                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    4                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    5                                                
                                            
                                                                                                            

                                
                                    Correct Answer: B
                                    
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    33.
                                    How many minimum states are required to find whether a string has odd number of 0
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    1                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    2                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    3                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    4                                                
                                            
                                                                                                            

                                
                                    Correct Answer: B
                                    
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    34.
                                    Consider alphabet ? = {0, 1}, the null/empty string ? and the sets of strings X0, X1 and X0.How are X1 and X2 are related ?
X0 = 1 X1

X1 = 0 X1 + 1 X2

X2 = 0 X1 + {?}

Which one of the following represents the strings in X0?
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    10 (0* + (10)*)1                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    10 (0* + (10)*)*1                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    10 (0* + (10)*)*1                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    10 (0 + 10)*1 + 110 (0 + 10)*1                                                
                                            
                                                                                                            

                                
                                    Correct Answer: C
                                    
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    35.
                                    Which of the following languages is/are regular?
L1: {wxwR ? w, x ? {a, b}* and ?w?, ?x? >0} wR is the reverse of string w

L2: {anbm ?m ? n and m, n?0

L3: {apbqcr ? p, q, r ? 0}
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    L1 and L3 only                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    L2                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    L2 and L3 only                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    L3 only                                                
                                            
                                                                                                            

                                
                                    Correct Answer: A
                                    
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    36.
                                    The set of all strings over ? = {a,b} in which strings consisting a
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    ab                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    a*bbb                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    (a+b)* bb                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    All of the mentioned                                                
                                            
                                                                                                            

                                
                                    Correct Answer: C
                                    
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    37.
                                    An individual token is called ________
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    Lexeme                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    Lex                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    Lexeme & Lex                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    None of the mentioned                                                
                                            
                                                                                                            

                                
                                    Correct Answer: A
                                    
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    38.
                                     Which of the following statement is correct?
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    A Context free language can be accepted by a deterministic PDA                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    union of 2 CFLs is context free                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    The intersection of two CFLs is context free                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    The intersection of two CFLs is context free                                                
                                            
                                                                                                            

                                
                                    Correct Answer: B
                                    Context-free languages are closed under the following operations. The Kleene star, the concatenation, the union and the intersection.
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    39.
                                    Which of the following pairs of regular expressions are equivalent?
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    1(01)* and (10)*1                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    x (xx)* and (xx)*x                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    x⁺ and x⁺ x^(*+)                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    All of the mentioned                                                
                                            
                                                                                                            

                                
                                    Correct Answer: D
                                    Rule (pq)*p=p (qp)*
Therefore
                                
                            
                        

                        
                            

                            
                            
                                                        
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                                    40.
                                    Which of the following are not regular?
                                

                                
                                                                                                                        
                                                
                                                
                                                
                                                    A                                                
                                                
                                                
                                                    String of )                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    B                                                
                                                
                                                
                                                    Palindromes Consisting of 0                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    C                                                
                                                
                                                
                                                    String of 0                                                
                                            
                                                                                    
                                                
                                                
                                                
                                                    D                                                
                                                
                                                
                                                    All of the mentioned                                                
                                            
                                                                                                            

                                
                                    Correct Answer: D
                                    Strings of odd number of zeroes can be generated by the regular expression (00) *0.Pumping lemma can be used to prove the non-regularity of the other options.
                                
                            
                        

                        
                            

                            
                            
                                                        
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