1. How are while and if control structures implemented in assembler?

2. Who was the famous computer scientists who wrote the paper "Goto Considered Harmful?"

3. What new methodology of programming appeared in the mid-1960s that replaced the older spaghetti code?

4. What CSC-1 instruction always appears at the "bottom" of a while loop?

5. Which CSC-1 instruction is often used as a "do-nothing" placeholder?

6. How many jumps must there be in every while loop?

7. Sketch out the skeleton of a while loop as implemented in CSC-1 assembler.

WHILE:    ....             ; check termination condition
          JZ    ENDWHILE   ; break out of loop if done
          ....             ; body of the loop
          JMP   WHILE      ; the instruction that makes it a loop
ENDWHILE: NOP              ; first instruction after the loop

8. When writing CSC-1 assembler code that implements an if statement, what instruction must appear before the ELSE?

9. How are relational comparisons such as x < y implemented in assembler?

10. If two numbers are equal what value results from their subtraction?

11. When you subtract A-B, what does it mean when the answer is negative?

12. What are improvements in code called?

13. The gcd program in Section 9.4 does not have any I/O. Why not?

14. How do many computers, such as those using the Motorola 68000 chip, actually perform input and output?

15. Write 2 lines of CSC-1 assembler which compare x != y.

LOD   X
SUB   Y
JZ    ENDWHILE

16. Declare two integer variables called m and n. They should have the initial values 12 and 19, respectively.

M:     NUM    12
N:     NUM    19

17. Which CSC-1 instruction should appear at the end of every program?

HLT

18. Write a tiny chunk of CSC-1 assembler which implements an if-then statement, one that has no else clause. Here's the C statements. (Don't worry about what is in the middle where the dots are. You could use a NOP if you want to.)

               if (x != y) {
                    ....
               }

IF:     LOD    X
        SUB    Y
        JZ     ENDIF
        ...
ENDIF:  NOP

19. Write a couple CSC-1 instructions which would implement the following C statement: (Assume that variables x and y have already been declared.)

               x = x + y;

      LOD   X
      ADD   Y
      STD   X

20. Write a couple CSC-1 instructions which would implement the following C statement: (Assume that all variables appearing in the C have already been declared.)

               y = x - z + w;

      LOD   X
      SUB   Z
      ADD   W
      STD   Y

21. Given the following fragment from the gcd program, why is x > y not implemented by a subtraction instruction?

        3:  IF:        JN    ELSE      ;      if (x > y)
        4:  THEN:      STD   X         ;           x = x - y;
        5:             JMP   ENDIF     ;
        6:  ELSE:      LOD   Y         ;      else
        7:             SUB   X         ;
        8:             STD   Y         ;           y = y - x;
        9:  ENDIF:     NOP             ;