KOI: Lab 1

Part A: Getting friendly with your compiler

Fix this large, meaningless program that doesn't work:

• The source code for a large, meaningless program that doesn't work.

Use a debugger to find out where the program crashes, and why. It's a rather large and intentionally obscure program, so it's probably hard to find the problem without a debugger.

Fix the problem and recompile the program, so it can execute without crashing. It's sufficient just to comment out lines that don't work.

Discuss:

1. Where was the problem?
2. Why did the program crash?
3. What did you do to fix the problem?

Part B: The simple compiler from chapter 2

Compile and try out these two programs from the course book. Make each of them a separate project:

• The source code for the program in section 2.5 of the course book.
• The source code for the very simple compiler in section 2.9 of the course book.

Both programs translate from infix to postfix notation.

Suggestion: When you execute the programs, start them from a command window. If you start text-based programs like these from inside Borland C++, or by clicking on the icon, all output disappears when the program exits and the window closes.

Discuss:

4. Which of the phases and other parts of a compiler are present in the 2.9 program?
5. How are they implemented?
6. Which are missing?
7. If you were to modify the 2.9 program so it actually calculates the values of the expressions, and not just prints out postfix code, how would you do that?

Part C: Recursive and not recursive

int plus(int x, int y) {
  return x + y;
}

#define PLUS(x, y) ((x) + (y))

int factorial(int n) {
  if (n == 0)
    return 1;
  else
    return n * factorial(n - 1);
}

Later in the course, you will come into contact with context-free grammars (which are recursive) and regular expressions (which are not). In that sense (but only in that sense!) context-free grammars are similar to C functions, and regular expressions are similar to C macros.

Some hints about the C preprocessor:

#define FOO 4711
i = FOO;

i = 4711;

#define TIMES(x, y) x * y
i = TIMES(7, 4);
i = TIMES(7, 2 + 2);
i = TIMES(++, {);

i = 7 * 4;
i = 7 * 2 + 2;
i = ++ * {;

#define SQR(n) n*n
#define CUBE(n) n*SQR(n)
i = CUBE(3);

i = 3*3*3;

Discuss:

8. Does the macro work?
9. Why, or why not?
10. If it doesn't work: Explain how the C preprocessor would have to be modified for the macro to work!

Report