Keunwoo Lee : CSE 142 : 21 October 1999

Pseudo-homework

1. On a scale of 1 (completely unprepared) to 5 (very well prepared), rate how well you think my sections prepared you for the exams and homeworks so far.
2. Which of the following would you like to see more of in my section? Which less? (Clearly mark which you want more of, and which less!)
   Lectures; HW review; group exercises; open or directed Q & A; other (specify)
   
3. Write one original comment that you don't think any other student will write. Constructive criticism about the section is best, but if you write about (say) Mondrian that's fine too.
   (Note: Mondrian was just an example of something completely random. It was meant to convey the idea that you could tell me anything you wanted. FYI he's a Modernist painter.)

Function review

• Do you understand the difference between a function definition and a function call?



• What is the difference between a parameter and a local variable?



• Consider the difference between the value of an argument passed to a function, and the value the parameter can attain within the function.



• Return values: a function can return any of the basic types, and it behaves exactly as if you had referenced a variable of that type.

Loops

You'll never grok loops until you write a few bad ones, so write a fragment that:

1. ...adds all the numbers from 1 to n inclusive, where n is a variable or a parameter that can be set to any number >= 1.

       /* One solution (assume n has been set): */
       int count = 1;
       int total = 0;
       while (count <= n) {
           total = total + count;
           count = count + 1;
       }
         

2. ...prints all the multiples of 3 between 0 and 20, inclusive.

       /* One solution: */
       int current = 0;
       while (current <= 20) {
           if (current % 3 == 0) {
               printf("%d ", count);
           }
           current = current + 1;
       }
   
       /* Another one that runs a little faster... */
       int current = 0;
       while (current * 3 <= 20) {
           printf("%d ", current * 3);
           current = current + 1;
       }
   
       /* A third solution, perhaps the most elegant */
       int current = 0;
       while (current <= 20) {
           printf("%d ", current);
           current = current + 3;
       }
         

3. ...prints an empty box of characters:

           *******************
           *                 *
           *                 *
           *******************

   of height h and width w.

       /* Once again, there are several ways.  Here's mine (BTW I'm
       deliberately showing off a different indent style): */ 
       int row_num = 1;
       int col_num;
   
       /* We want to print h rows... */
       while (row_num <= h)
       {
   
           /* For each row, we start over at column number 1 */
           col_num = 1;
   
           /* For first and last lines, print a full row of stars */
           if (row_num == 1 || row_num == h) 
           {
               while (col_num <= w)
               {
                   printf("*");
                   col_num = col_num + 1;
               }
           }
           else /* For all the other rows, print something different: */
           {
               /* Print first star and advance colum */
               printf("*"); 
   
               /* Now print h - 2 spaces */
               while (col_num <= h - 2)
               {
                   printf(" ");
                   col_num = col_num + 1;
               }
   
               /* Print last star */
               printf("*"); /* Opening star */
           }
   
           /* Print newline and advance to next row. */
           printf("\n"); 
           row_num = row_num + 1;
       }
         

4. ...prints the Fibonacci sequence 1, 1, 2, 3, 5, 8..., asking the user if (s)he wants another number after each iteration. Use 0 for no, 1 for yes.

       /* Faking a boolean type for convenience & readability */
       #define TRUE  1
       #define FALSE 0
   
       /* We'll use these to keep a running total. */
       int current = 1, last = 0;
   
       /* Initially, we want to continue. */
       int continue = TRUE;
      
       while (continue == TRUE) {
           /* Print the current fibonacci number. */
           printf("current: %d\n", current);
   
           /* Add the previous number to get the next in the sequence,
           and save the current number in last for next time. */
           current = current + last;
           last = current;
   
           /* Ask the user if (s)he wants to continue. */
           printf("Enter 1 to continue, 0 to quit: ");
           scanf("%d", &continue);
       }