program    ---->  { stmt }

     stmt       ---->  "{" { stmt } "}" | ifstmt | whilestmt |

                       assign ";" | readstmt ";" | writestmt ";" | writecstmt ";"

     ifstmt     ---->  "IF" "(" expr ")" stmt [ "ELSE" stmt ] 

     whilestmt  ---->  "WHILE" "(" expr ")" stmt 

     assign     ---->  id "=" expr  

     readstmt   ---->  "READ" "(" id ")"

     writestmt  ---->  "WRITE" "(" expr ")"

     writecstmt ---->  "WRITEC" "(" intconst ")"

     expr       ---->  mulexpr { ( "+"|"-" ) mulexpr } 

     mulexpr    ---->  unaryexpr { ( "*"|"/"|"%" ) unaryexpr } 

     unaryexpr  ---->  const | id | "(" expr ")"

     const      ---->  intconst


     (Supplied by scanner: Everything in "", id, intconst)
     (Metasymbols: | means "or", { xx } means "zero or more occurrences of xx,
      [ xx ] means "optional item xx", that is, zero or one occurrences of xx,
      ( x | y ) means "either x or y", where () is used for grouping.
      ----> has precedence over | which has precedence over everything else.)

1. Implement the WHILE loop (before IF-ELSE, since it is easier).

   As described in class, if you have source like the following:

   WHILE ( expr ) stmt

   then output the following quadruples (here nextQuad is the next quadruple to be generated):

   
          Store value of nextQuad in local variable whilestart
   
          Quads to evaluate expr, with result in temporary T1
   
          Store value of nextQuad in local variable jeqquad
   
          (JEQ, T1,   , __ )      (Location __ must be backpatched.)
   
          Quads for stmt
   
          (JMP,   ,   , whilestart)
       
          Backpatch quad number jeqquad to put value nextQuad into 4th position
   

   You could use the following simple source to check the new WHILE loop: source.

2. Implement the IF-ELSE.

   Again as described in class, if you have source like the following:

   IF ( expr ) stmt1 [ ELSE stmt2 ]

   then output the following quadruples:

   
          Quads to evaluate expr, with result in temporary T1
   
          Store value of nextQuad in local variable (for backpatching)
   
          (JEQ, T1,   , __ )      (Location ___ must be backpatched.)
      
          Quads to evaluate stmt1
   
          If there is no ELSE, then backpatch value of nextQuad into earlier JEQ.
   
          If there is an ELSE, then
             Store value of nextQuad in local variable (for backpatching)
             (JMP,   ,   , __ )   Location __ must be backpatched
             Backpatch value of nextQuad into ealier JEQ
         
             Quads for stmt2
   
             Backpatch value of nextQuad into earlier JMP.
   

   I used following simple source to check the new IF-ELSE loop: Source.

  Source to use Newton's method to calculate the square root of 2..

Here is simple source to try out the Project IV work:

  Source to generate Fibonacci numbers and identify them as even (E) or odd(O).

Here is very complicated source for the Project IV work:

  Source to generate Fibonacci numbers, to factor them, and print the results.