Homework Exam

1
Homework / Exam

• Continuing KR Chapter 6
• Exam 2 after next class
• Open Book / Open Notes
• Up through end of KR 6.4 plus MAKE

2
Review structs

• struct point
• int x
• int y
• pt
• struct point pt1, pt2
• struct point maxpt 320, 200

3
Review structs

• struct rect
• struct point pt1
• struct point pt2
• ? Note must have following
• struct rect box

4
Review structs

• box.pt1.x 5
• box.pt1.y 10
• box.pt2.x 10
• box.pt2.y 20
• area (box.pt2.x box.pt1.x)
• (box.pt2.y box.pt1.y)

5
What can we do with a struct?

• Reference members
• box.pt2.x box.pt1.x width
• Assign as a unit
• pt2 pt1
• Create a pointer to it
• struct point ppt1
• ppt1 pt1

6
What can we do with a struct?

• Not legal to compare structs
• if (pt1 pt2) ? INVALID
• Must be done as
• if (pt1.x pt2.x pt1.y pt2.y)

7
structs and Functions, KR 6.2

• / ptinrect
• if point p in rect r, return 1 else return 0
• note slightly different from KR example /
• int ptinrect (struct point p, struct rect r)
• return p.x gt r.pt1.x p.x lt r.pt2.x
• p.y gt r.pt1.y p.y lt r.pt2.y

8
Arrays of structs, KR 6.3

• Multiple related arrays
• char keywordNKEYS
• int keycountNKEYS
• Can be implemented as an array of structs
• struct key
• char word
• int count
• keytab NKEYS

9
Arrays of structs

• Alternative array of structs implementation
• struct key
• char word
• int count
• struct key keytabNKEYS

10
Arrays of structs

• Initialization for an array of structs
• struct key
• char word
• int count
• keytab
• auto, 0,
• while, 0
• / NKEYS is dynamically derived /

11
Size of structs

• sizeof is a compile-time unary operator
• Can be used to get integer (actually size_t)
• sizeof object
• sizeof (type name)
• Applied to structs
• define NKEYS (sizeof keytab / sizeof (struct
  key))
• define NKEYS (sizeof keytab / sizeof keytab0)

12
Pointers to structs, KR 6.4

• Declare and initialize a pointer to struct
• struct point p
• struct point pp p
• Refer to members of struct p via pointer pp
• (pp).x and (pp).y ? See precedence
• More commonly done as
• pp-gtx and pp-gty ? See precedence

13
Pointers to structs

• struct string
• int len
• char cp
• p
• Expression Same as Value / Effect
• p-gtlen (p-gtlen) increments len
• p-gtcp (p-gtcp) value is a char
• p-gtcp ((p-gtcp)) value is a char
• increments cp

14
Pointers to structs

• / ptinrect (pointer version)
• if point p in rect r, return 1 else return 0 /
• int ptinrect (struct point pp, struct rect rp)
• return pp-gtx gt rp-gtpt1.x pp-gtx lt rp-gtpt2.x
• pp-gty gt rp-gtpt1.y pp-gty lt rp-gtpt2.y