EXERCISES ON STRUCTURES

READING 
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Kernighan and Ritchie, 6.1
Sedgewick, 69-80

SUPPLEMENTAL READING
--------------------
Deitel and Deitel, 10.1-10.6

EXERCISES
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1. What is wrong with the following C declarations?
 
        A.   struct ex ( float a, b )
        B.   struct ex { float a, float b };
        C.   struct ex { float a; int b }
        D.   struct ex { int a; float b; };
        E.   struct ex { int a; int b; }

2. What is the difference between the following two programs?

          #include <stdio.h>
          struct interval { float a; float b; };
          void main()
            {  struct interval test;
               test.a = .25; test.b = .75;
               printf("[%6.4f %6.4f]\n", test.a, test.b);
            }

          typedef struct { float a; float b; } interval;
          void main()
            {  interval test;
               test.a = .25; test.b = .75;
               printf("[%6.4f %6.4f]\n", test.a, test.b);
            }

3. Provide implementations of a function NEW (return an interval, 
   given two floats) and a function SHOW (print an interval) so that
   the following "main" is functionally equivalent to the two programs
   in exercise 2.

          main()
            { interval test = NEW(.25, .75); show(test); }

4. Write a function that returns 1 if a float falls within an interval,
   0 if not.  Use the type "interval" defined in exercise 3, and the
   function prototype "int in(float, interval);"

5. Define a type for rectangles that are parallel to the axes in a
   Cartesian coordinate sysytem. Use the type "interval" from exercise 3.

6. Write a function that returns 1 if a point falls within a rectangle,
   0 otherwise. Use the function prototype "int inrect(point, rect);" and
   define your own point type.

7. What is wrong with the following C declarations?
 
        A.   typedef struct { float x; float y } point;
        B.   typedef { float x; float y; } point;
        C.   typedef struct { float x; float y; };
        D.   typedef struct { float x; float y; } point;
.
.
		  ANSWERS TO EXERCISES ON STRUCTURES


1.
        A. Everything. Need braces, not parens; semicolons, not comma.
        B. Comma is wrong (need semicolons).
        C. Need semicolon after b.
        D. Nothing wrong. This one is OK.
        E. Need semicolon at end.
                 
2. None

3. 
          #include <stdio.h>
          typedef struct { float a; float b; } interval;
          interval NEW(float a, float b)
            {
              interval t;
              t.a = a; t.b = b;
              return t;
            }
          void show(interval t)
            {
               printf("[%6.4f %6.4f]\n", t.a, t.b);
            }

4. 
          int in(float p, interval t)
            {
              if (p < t.a) return 0;
              if (p > t.b) return 0;
              return 1;
            }

5.
          typedef struct { interval x; interval y; } rect;

6.
          typedef struct { float x; float y; } point;
          int inrect(point p, rect t)
            {
              return in(p.x, t.x) && in(p.y, t.y);
            }


7. 
        A. Semicolon missing after "y".
        B. "struct" missing; some type must follow "typedef".
        C. Useless because there is no name for the typedef
        D. Nothing wrong.  This one is OK.