Organization of Programming Languages
Answers to On-line Quiz #1              January 27, 1997


Rewrite the following conditionals as sequential choices by using
the else-if form instead.

1. (10 pts)
if c >= 5 then
  if c > 5 then S1
else S2

if c<5 then S2
elseif c > 5 then S1

2. (10 pts)
if cnt > min then
   if cnt < max then S1
   else S2 end
end

if cnt> min and cnt< max then S1
elseif cnt > min then S2

3. (10 pts) For each of the following paradigms,
   give the names of 3 popular programming languages

    a) imperative: C, PASCAL, Modula

    b) functional: Lisp, Scheme, ML

    c) object-oriented: C++, Smalltalk, Java
  

4. (10 pts) 
What are the three major phases of compilation? Which of these
      phases is/are not part of interpretation?

1) Lexical analysis
2) Syntatic analysis
3) Code generation
The last phase is not part of interpretation.

5. (25 pts) 
Given the following abstract-syntax-tree, write the corresponding notations
 
    a) prefix: mod * a b + c * d e

    b) postfix: a b * c d e * + mod

    c) infix: (a * b) mod (c + (d * e))
   
              mod
             /   \
            *     +
           / \   / \
          a   b c   *
                   / \
                  d   e

6. (20 pts)  Give a grammar that generates all binary numbers,
     that is, strings of 0s and 1s. Numbers should have no
     leading 0s except the number 0. Then give a derivation for 1011.

S -> 1L | 0
L -> 0L | 1L  | <empty>

S -> 1L -> 10L -> 101L -> 1011L -> 1011

7.  10pts
a. Give the grammar rules for conditional statements in
 a language like C or Pascal. Is your grammar ambiguous, yes or no?

S -> if E then S
S -> if E then S else S
Yes, this is ambiguous.
We can not always identify for each else the matching if.

b. Give the rules where the conditionals end with the word endif.
is this grammar ambiguous, yes or no?

S -> if E then S endif
S -> if E then S else S endif
No, this is  not ambiguous.
We can always identify for each else the matching if.

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