Introduction to Programming in C

1
Chapter 12

• Introduction to Programming in C

2
Pointer Arithmetic

• A pointer variable can be hold the address of an
  array element. Declare the variables
• int a8, p
• And then set the pointer to the address of a0
• p a0
• Now we can store an integer value in a0 by
  doing either of the following
• a0 5
• p 5 / Both do the same thing /

p
a
0
0
0
0
5
0
0
0
0 1 2 3 4
5 6 7
3
Pointer Arithmetic

• int p
• p or (p) Value is p, but then p increments
• (p) Value is p, but then p increments
• p or (p) Increment p first, then value is
  p
• p or (p) Increment p first, then value is
  p

4
Pointer Arithmetic

• What does each of these do?
• int sum 0
• for (p a0 p lt a8 p)
• sum p
• q 15
• (q)
• printf(d,q)
• q

q
p
a
49
16
9
1
0
36
25
4
0 1 2 3 4
5 6 7
5
Pointer Arithmetic

• What does each of these do?
• int sum 0
• for (p a0 p lt a8 p)
• sum p / sum 140 /
• q 15 / a1 15, q a2 /
• (q) / a2 5
• printf(d,q) / q a3, print 9 /
• q / a3 becomes 10 /

q
p
a
49
16
9
15
0
36
25
5
0 1 2 3 4
5 6 7
6
Pointers and Arrays

• We can use an array name as a pointer. These do
  the same thing
• p a0
• p a
• Note that the loop
• for (p a0 p lt a8 p)
• sum p / sum 140 /
• Can be replaced by this
• for (p a p lt a 8 p)
• sum p

p
a
49
16
9
1
0
36
25
4
0 1 2 3 4
5 6 7
7
Pointer Arithmetic

• What does this do?
• int sum 0
• p a
• while (p lt a8)
• sum p / sum 145 /

p
a
49
16
9
15
0
36
25
5
0 1 2 3 4
5 6 7
8
Pointer and Arrays - Homework

• P. 235 1, 3, 8, 9,12 (mail code in for 12).

9
8

• include ltstdio.hgt
• define N 100 / Max length of string /
• main()
• char aN, p
• printf("Enter a message ")
• p a
• scanf ("c", p)
• while (p ! '\n')
• p
• scanf ("c", p)
• while (p gt a)
• printf("c", p--)
• printf("\n")

10
12

• define N 10
• main()
• float p
• float identNN
• int col, row 0
• p ident00
• p 1.0
• for(p ident01 p lt identN-1N-1
  p)
• row
• if (row N1)
• p 1
• row 0
• else
• p 0

11
9

• define N 100 / Max length of string /
• main()
• char aN, p, q
• / What goes here?? /
• return 0

12
Program 12

• 9, P. 237

13
9

• define N 100 / Max length of string /
• main()
• char aN, p, q
• printf("Enter a message ")
• p a
• scanf ("c", p)
• while (p ! '\n')
• if (((p gt 'A')(p lt 'Z')) ((p gt
  'a')(p lt 'z'))) p
• scanf ("c", p)
• p--
• q a
• while (p gt q)
• if (p q)
• p--