L-34 MCS 260 Wed 7 Nov 2001

Exam II on Chapters 5 to 8

Consider

    int value ( char c );
    /* returns 26, 25, .. , 1 if c equals respectively A, B, .. , Z;
       returns 0 for any character that is not a capital letter  */

Give the definition of the function value :

    int value ( char c )
    {
       if ((c >= 'A') && (c <= 'Z'))
          return 'Z' - c + 1;
       else
          return 0;
    }

                                                        +--------+
                                                        |    /10 |
                                                        +--------+

Write a program that reads in a sequence of characters and that prints out the same sequence, except that all characters with ASCII code 13 must be replaced by a newline.

     #include<stdio.h>

     int main ( void )
     {
        int c;

        while ((c = getchar()) != EOF)
           if (c == 13)
              putchar('\n');
           else
              putchar(c);
 
        return 0;
     }

                                                        +--------+
                                                        |    /15 |
                                                        +--------+

Consider

    double value ( int q, int d, int n, int p );
    /* returns the value of the given number of coins, where
          q = number of quarters (value is $0.25 apiece),
          d = number of dimes    (value is $0.10 apiece),
          n = number of nickels  (value is $0.05 apiece), and
          p = number of pennies  (value is $0.01 apiece).    */

Give the definition of the function value :

    double value ( int q, int d, int n, int p )
    {
       double val;

       val = q*0.25l + d*0.10l + n*0.05l + p*0.01l;

       return val;
    }

                                                        +--------+
                                                        |    /10 |
                                                        +--------+

The octal number system uses the digits 0,1,2,3,4,5,6,7.

Give the octal representation of the decimal number 54: 66 because 54 % 8 = 6 and 54/8 = 6

Give the definition of the following function

  void write_octal ( int n );
  /* writes the integer n in the octal number system,
     starting with the least significant digit (thus backwards) */

  void write_octal ( int n )
  {
     int wn;

     for (wn = n; wn > 0; wn /= 8)
        printf("%d", wn % 8);
  }

                                                        +--------+
                                                        |    /15 |
                                                        +--------+

Variables of an enumeration type day24 take the following values :

       { morning, noon, afternoon, evening, night }.

In a 24 hour day, the morning starts at 6 (= 6AM), noon at 11 (= 11AM), the afternoon at 13 (= 1PM), the evening at 19 (= 7PM), and the night at 21 (= 9PM).

Give the C definition of day24 ensuring that the values of the enumeration type correspond to the respective numbers 6, 11, 13, 19, and 21.
```
        enum day24 { morning=6, noon=11, afternoon=13, evening=19, night=21 };

        typedef   enum day24   day24;
```

Write an input function read for the type day24, using the prototype

  void read ( day24 *dt );
  /* scans a floating point number t, using the convention that 
        for  6 <= t < 11, we call this time of the day morning;
        for 11 <= t < 13, noon; for 13 <= t < 19, afternoon;
        for 19 <= t < 21, evening, and otherwise we call it night. */

Give the definition of read below :

  void read ( day24 *dt )
  {
     float t;
 
     scanf("%f", &t);

     if ((t < 6) && (t > 21)) *dt = night;
     else if (t < 11) *dt = morning;
     else if (t < 13) *dt = noon;
     else if (t < 19) *dt = afternoon;
     else *dt = evening;
  }

                                                        +--------+
                                                        |    /25 |
                                                        +--------+

Consider the following program, using the function R :

     void R ( int *p );
     #include<stdio.h>
     int main(void)                          void R ( int *p )
     {                                       {
        int a = 3;                              static int cnt = 0;
        R(&a);                                  int i = *p * ++cnt;
        R(&a);                                  *p += i;
        printf("%d", a);                     }
        return 0;
     }

Make a diagram representing all variables in main and R. Illustrate with the diagram what happens before, during, and after each call of R(&a). What is printed?

                    variables
--------------------------------------------------------
             in main    |            in R
========================================================
  before     a          |             cnt
   first     +----+     |              +---+
   call      |  3 |     |              | 0 |
             +----+     |              +---+
                        |
  during     a          |   p         cnt      i
   first     +----+     |   +-----+    +---+   +----+
   call      |  3 |<--------|- &a |    | 1 |   |  3 |
             +----+     |   +-----+    +---+   +----+
                        |
  during     a          |   p         cnt      i
  second     +----+     |   +-----+    +---+   +----+
   call      |  6 |<--------|- &a |    | 2 |   | 12 |
             +----+     |   +-----+    +---+   +----+
                        |
  after      a          |             cnt
  second     +----+     |              +---+
   call      | 18 |     |              | 2 |
             +----+     |              +---+
                        |

  18 is printed
                                                        +--------+
                                                        |    /25 |
                                                        +--------+

FINAL EXAM is in Lecture Center C6 on Monday 3 December 2001 from 1:00 till 3:00PM.