Gate Compiler Design

Question

Consider the following grammar

E → E+T/T

T → T*F/F

F → id/(E)

Calculate Lead and Last for every Non terminal.

Comments

from where u got this ???

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Please solve it it is very important and basic question i know tht but i m having confuse. i beg you please solve i m very poor guy and i havent done coaching like you all guys over here.

thank you so much in advance please solve.

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No gate question or any other questions will be in this way

Answer 1

Lead :- Lead is a list of all those terminals symbols("operators") which can appear first on any right hand side of a production.

For each non-terminal i.e. left hand side,a Lead list containing the first terminal in each production for that non-terminal.Where a non-terminal is the first symbol on the right hand side, include both it and the first terminal following.e.g. for

X $\rightarrow$ a.... / Bc

includes a,c and B in X's Lead List.

Trail:- Trail or Last is a similar list of those terminals which can appear Last.

For each non-terminal i.e. left hand side,a Last or trail list containing the last terminal in each production for that non terminal.Where a non-terminal is the last symbol on the right hand side, include both it and the last terminal .e.g. for

Y $\rightarrow$ ....u / ....vW

includes u,v and W in Last or Trail list.

 

Now for the given Grammar

Lead(E) ={ + , * , id , (   }               Last={ + , * ,  id , )  }

Lead(T) ={ * , id , (   }                    Last={ * , id , )   }

Lead(F)={ id , ( }                            Last={ id , ) } 

 

Comments

@shivani did u got answer or shud i tell...this is not gate type question...but it can appear in ISRO exam....///@sharma ji it wud have been ..better if you wud have explained step by step...for evry non-terminal plz update it

Answer 2

Lead(E) ={ ( +,*,id}                  Last(E) ={ +,*id, ) }

Lead(T) = { *,id,( }                Last(T) ={ *,id, ) }

Lead(F) = { id,( }                 Last(F) ={ id, ) }

Comments

no, first follow and lead trail both are different.

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@shivani I think Lead(E)={+,*,id,(} , isnot it?

http://cs.stackexchange.com/questions/4716/understanding-leading-and-trailing-operations-of-an-operator-precedence-grammar

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@alokthebranded How you can select the answer as best without confirmation ? Please don't select any answer until you are not confirm about the answer. Your one mistake can misguide people here. 

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Sir i have seen your hardwork and skill for each and every question so i think whatever you solve would be right.

sir i m just waiting for some days and once i will collect money then i will join coaching then i myself will solve and post various answers:)

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i mean before selected mine you selected answer of  shiivani which was wrong.

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Respected sir ,

because she answered infront of you only

and you dint say to her anything ...that there's mistake in the answer 

so i assumed that she answered right . 

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and it is not necessary i am always right because i am not a expert.

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ohh okie Respected sir

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I have updated the answer here too chk @Leen :)

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@ Leen sir 

and sir you are scolding me just.this thing is hurting me. shivani mam when wrote wrong answer then you should also scold her that without thinking properly and without solving properly how can you write anything in the answer.

the person who wrote the answer can only misguide the people sir.

you are not fair with me sir but its okie sir jee ap bade hai . apki bahut zyada respect karne laga hu mein. aur mein bahut zyada chota hu isliye apko sahi manta hu. bus baat dil ko lagi to kehdi :)

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srestha Last(E) and Last(T) are wrong. check my Answer.

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@alok Are My dear , we r not scolding. But here we r to guide each other in a better way, right?. So, if one not getting the answer , other could find the way, if one do some mistake ,other could take in a right way. So, be happy - we all are for each other .

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alokthebranded without posting the answer how she did know that her answer was right or wrong .but you selected it and she thinks she was right and other users will also think the same that selected answer is right.

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alokthebranded are itna preshan hone ki jaroorat nhi h.be cool be happy 

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yes rt @Leen