Got Questions? Try office hours, email or the class newsgroup.

1. Rewrite the following C code fragment without using goto or break:
   
       j = -3;
       for ( i=0; i<3; i++ ) {
           switch (j+2) {
               case 3:
               case 2: j--; break;
               case 0: j+=2; break;
               default: j=0;
           }
           if (j>0) break;
           j=3-i;
       }

 
2. Devise a program in a language of your choice to determine at runtime the relative precedence and associativity of the multiplication and addition operators. Do the same thing for less-than and boolean or. Your program should produce output something like this:
   
           * has higher precedence than +
           * is left associative
           + is right associative

 
3. Consider the following Algol 60-style for statement:
   
       for i := j+1 step i*j until 3*j do j:= j+1
   
   Assume the initial value of j is 1. List the sequence of values that i assumes during execution of this loop assuming the following semantics:
   
       a. All control expressions are evaluated once at loop entry.
       b. All control expressions are evaluated at the beginning of each iteration.
       c. step expression are evaluated once on loop entry but until expressions are evaluated each time.
       d. until expressions are evaluated once on loop entry but step expressions are are evaluated each time.

 
4. The Bohm-Jacopini Result proves that gotos are unnecessary in the sense that any program (flowcharts, actually) with gotos can be rewritten using three constructs: 1) statement sequences, 2) if statements, 3) while statements. Actually you don't even need if! Show how any if statement can be rewritten using a while loop. In other words, show how:
   
       if E then S
   
   can always be transformed to an equivalent form:
   
       while E' then S'
   
   (You need to tell me what E' and S' look like in terms of E and S.)

 
5. Ok. Get your Web browsers ready for this question! Find a reference or tutorial for Fortran 90 somewhere on the Web and rewrite the following code as a multiple selection (case, switch) statement in Fortran 90:
   
       if (k=1) or (k=2) then j:=2*k-1
       if (k=3) or (k=5) then j:=3*k+1
       if (k=4) then j:=4*k-1
       if (k=6) or (k=7) or (k=8) then j:=k-2
   
   Assume that all variable are integer type.

 
6. PL/I has a wild feature that allows labels (goto targets) to be assigned to variables and passed into procedures so you can do things like this (this isn't precise PL/I syntax, just pseudo-code):
   
       if ( A > B ) 
           MY_LABEL = L100;
       else 
           MY_LABEL = L200;
       ...
       goto MY_LABEL;
   
   Describe a situation where this might be useful and briefly discuss its merits (advantages and disadvantages) as a language feature.
   
   
7. EXTRA CREDIT: Rewrite the following super-weird C code using if-else statements. Feel free to experiment by running similar examples or check C reference material.
   
        int a, b, c, d, e;

    a?b:c;
    a?b:c?d:e;
    a?b?c:d:e;
    a?b:c?d:e;