Lect 11P. 1

1
Arrays

• Lecture 11

2
What Is an Array?

• An array is a group of items of the same type
  under one variable name. It is an ordered list
  of elements where each is of the same data type.
• As an example, the days of the week can be
  represented as a one-dimensional array named day
  where Sunday is the first element, Monday the
  second, and so on.

3
Thinking About Arrays

• The days of the month can be thought of as a
  two-dimensional array. Looking at a calendar,
  each row represents a week (which can be
  represented as a one-dimensional array), and the
  entire month is composed of an array of arrays,
  that is, a two-dimensional array.

4
Arrays

• Taking the concept further, the days of the year
  can be represented as a three-dimensional array,
  that is, an array of arrays of arrays. The first
  dimension is the day of the week, the second the
  week of the month, and the third the month of the
  year.

5
Declaring Arrays

• A one-dimensional array is represented by
  specifying the array name followed by a number in
  square brackets to indicate the array size
  (or number of elements).
• The statement
• int day 7
• would declare a seven element array of integers.
• Declaring multi-dimensional arrays is similar
  int month 4 7 would declare an array of
  integers with 4 rows and 7 columns.

6
Assigning Values to Arrays

• Once an array is declared, the elements are
  accessed by specifying the array name and the
  number of the element. In C, the first element
  is number 0, so a seven element array would have
  elements numbered 0 through 6.
• For the week of February 3 through 9 the array
  could be assigned as follows
• day03 day14 day25
  day36 day47 day58 day69
• The number in the brackets is called an index (or
  a subscript).

7
Assigning Values to Arrays

• Optionally, the array can have values assigned to
  its elements when the array is declared.
• For example, the statement
• int day 7 2, 3, 4, 5, 6, 7, 8
• declares a seven element array day and
  initializes (assigns values to) all seven of the
  elements.
• The program on the next slide illustrates how
  that works.

8
Program Example for Arrays

• /The following program will declare the array
  day, assign values to the elements, and print
  the data to the screen. /
• include ltstdio.hgt
• void main ( )
• int n, day 7 2, 3, 4, 5, 6, 7, 8
• for (n 0 n lt 7 n )
• printf ("day d is February d, 2004
  \n",
• n, dayn )

9
Program Output of an Array

• When this program is run, it will produce the
  following output
• day0 is February 2, 2004
• day1 is February 3, 2004
• day2 is February 4, 2004
• day3 is February 5, 2004
• day4 is February 6, 2004
• day5 is February 7, 2004
• day6 is February 8, 2004

10
Another Program Example

• / Program to generate an array of 10 random
  numbers /
  
• include ltstdio.hgt
• include ltstdlib.hgt
• define SIZE 10 / SIZE defined as symbolic
  constant /
• void main ( )
• int i, numbers SIZE
• for (i 0 i lt SIZE i )
• numbers i rand ( )
• printf ( "The number d is d \n", i,
  numbers i )