Question

Please answer for all 3 questions. Thanks.

Question 35 In a bottom up parser, what does it mean to perform a shift action? Answers: bits are moved n digit positions to the left/right values are popped from the parser's stack the next input token is placed onto the parser's stack lowercase characters are converted to uppercase characters bottom up parsers don't perform shifts, top down parsers do Question 37 What does S represent in LL parser? Answers: dollar sign end of input marker terminal symbol nonienir yml Question 38 Which of the following is a non-Terminal? Answers: + 2 exp

Answer 1

answer 35. shift operation:- in this operation the next input token is places on the parser's stack

Stack Input Buffer id+id+id$ Parsing Action Shift Reduce by S ->id Shift Shift Sid $S +id+id$ id+id$

as we can see that in this shift operation one token from the input is taken off and placed in the stack.

37. $ is used to indicate the end of input in every parser. so in LL also $ is used to show empty stack.

38. Non terminal - non terminal are the entities which can be expanded or they can be found at left hand side of a derivation. consider following example

exp -> n+n

exp->n*n-n

so as you can see that exp can be replaced by other terms so exp is a non terminal . similarly in our question too exp is a non terminal and this can be identified by the given grammar.

also + , - * are the operators so they can not be expanded so they are known as terminals . and $ is used for end of input.

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