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+14 votes
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To evaluate an expression without any embedded function calls

  1. One stack is enough
  2. Two stacks are needed
  3. As many stacks as the height of the expression tree are needed
  4. A Turing machine is needed in the general case
asked in Compiler Design by Veteran (68.8k points) | 1.1k views

2 Answers

+13 votes
Best answer
Expression without any calls in it $=> 1+2*3-4$

Expression with embedded calls $=> 1 + fun1(a,b,c) *fun2(3.4,58) - fun3(x,yz)$;

First we can convert Infix to Postfix using single stack (Using it as operator stack)

Then we can evaluate that expression using Single stack.
answered by Veteran (48.6k points)
edited by
how will you multiply using single stack ?
Does answer makes more sense now ? Amar ? I updated it .
what u think , embedded calls mean here ? I think, it mean like mul(a,b)   , add(5,6) .. mean operations itself..
Expression without any calls in it => 1+2*3-4

Expression with embedded calls => 1 + fun1(a,b,c) *fun2(3.4,58) - fun3(x,yz);
Ok, now it makes sense.. :)

And in general , when embedded calls allowed  ?   2 stacks ?
Why Turing machine is not needed, a TM can also perform required function i.e it can evaluate the expression  1+2*3-4 also, by Turing Thesis.

Is this the fact that, a stack is used for postfix evaluation of expression and also each function will have there own stack, so option A is correct?

How to decide here, a TM also does the job for us right?
What if questions says "WITH EMBEDDED FUNCTION CALLS"?

rahul sharma 5 : In that case Two stacks $First \ one \ works \ as \ Operator  \ stack$ and second one will be used to resolve function calls : 
Example : main(){                                     

int x=3,y=4,result;

result=addvalues(3,4)

}

addvalues(int v1,int v2)

return v1+v2;

functions                                          |  Operator    \
addvalues()                                        |    4              \
main()                                                 |3                 \                        7

 

Hello Anil

It's job of Pushdown automata (PDA) to evaluate an expression.

When you can do it using PDA. So in general case PDA is used not TM.
–1 vote
ans a)
answered by Boss (5.1k points)
postfix .is done by one stack. computer like postfix evalution.. .so ans is (a)...


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