Array II

1
Array II

• WEEK 10
• DEPARTMENT OF COMPUTER SCIENCE
• FACULTY OF SCIENCE AND TECHNOLOGY
• ASSUMPTION UNIVERSITY

2
Agenda

• Multi-dimensional arrays
• Multi-dimensional arrays and nested loops
  matrix computation
• Searching through an array using linear search
• Sorting elements of an array using bubble sort
• Examining bubble sort algorithm

3
Multidimensional Arrays

• Multidimensional arrays can be described as
  "arrays of arrays".
• For example, a bidimensional array can be
  imagined as a bidimensional table made of
  elements, all of them of a same uniform data
  type.
• jimmy represents a bidimensional array of 3 per 5
  elements of type int. The way to declare this
  array in C would beint jimmy 35

4
Multidimensional Arrays

• The way to reference the second element
  vertically and fourth horizontally in an
  expression would be jimmy13

5
Multidimensional Arrays

• Multidimensional arrays are not limited to two
  indices (i.e., two dimensions).
• They can contain as many indices as needed.
• Be careful! The amount of memory needed for an
  array rapidly increases with each dimension. For
  examplechar century 100365246060de
  clares an array with a char element for each
  second in a century, that is more than 3 billion
  chars. So this declaration would consume more
  than 3 gigabytes of memory!

6
Multidimensional Arrays

• Multidimensional arrays are just an abstraction
  for programmers, since we can obtain the same
  results with a simple array just by putting a
  factor between its indicesint jimmy 35
  // is equivalent toint jimmy 15 // (3 5
  15)
• With the only difference that with
  multidimensional arrays the compiler remembers
  the depth of each imaginary dimension for us.
• Take as example these two pieces of code, with
  both exactly the same result. One uses a
  bidimensional array and the other one uses a
  simple array

7
Multidimensional Arrays

• Multidimensional Array
• define WIDTH 5
• define HEIGHT 3
• int jimmy HEIGHTWIDTH
• int n,m
• int main ()
• for (n0nltHEIGHTn)
• for (m0mltWIDTHm)
• jimmynm(n1)(m1)
• return 0

Pseudo-multidimensional Array define WIDTH
5 define HEIGHT 3 int jimmy HEIGHT
WIDTH int n,m int main () for
(n0nltHEIGHTn) for (m0mltWIDTHm)
jimmynWIDTHm(n1)(m1) return 0
8
Multidimensional Arrays

• None of the previous two source codes produce any
  output on the screen, but both assign values to
  the memory block called jimmy in the following
  way

9
Multidimensional Arrays

• We have used "defined constants" (define) to
  simplify possible future modifications of the
  program. For example, in case that we decided to
  enlarge the array to a height of 4 instead of 3
  it could be done simply by changing the
  linedefine HEIGHT 3 todefine HEIGHT 4
  with no need to make any other modifications to
  the program.

10
Multidimensional Arrays and Nested Loops

• It is also possible to create arrays with two or
  more dimensions.
• Two dimensional arrays are useful for storing
  matrices.// two ways of creating two
  dimensional arraysint matrix 0, 1, 2,
  3, 4, 5, 6, 7, 8, 9, 10,
  11int square new int55// creates
  5 by 5 matrix with zero values

11
Multidimensional Arrays and Nested Loops

• Taking the previous 2D array matrix as an
  example, in order to perform operations on each
  value of a multi-dimensional array, it is
  necessary to nest several for loops.
• The example code below sets every entry of matrix
  to 1. for (int i0 ilt3 i) for (int j0
  jlt4 j) matrixij 1

12
Linear Search

• Linear search is a part of integer arrays which
  helps user to find the number entered by him and
  tells him the exact location of the number.

13
Linear Search

• include ltiostreamgt
• using namespace std
• int main(void)
• int list30, num, n, i
• cin gtgt n
• for (i0 iltn i)
• cin gtgt listi
• cout ltlt "Enter the number to be searched"
• cin gtgt num
• for (i0 iltn i)
• if (listinum)
• break
• cout ltlt "The number was found at " ltlt i
• system("PAUSE")

14
Bubble Sort

• Sorting is the method of arranging the elements
  of an array in an order (ascending or
  descending).
• In the bubble sort, the list in any moment is
  divided into two sublists sorted and unsorted.
• The smallest element is bubbled from the unsorted
  sublist and moved to the sorted sublist.

15
Bubble Sort
16
Bubble Sort

• include ltiostreamgt
• using namespace std
• int main(void)
• int temp, i, j
• int ar10
• cout ltlt "Enter elements of array\n"
• for (i0 ilt10 i)
• cin gtgt ari

17
Bubble Sort

• for (i0 ilt10 i)
• for (j10-2 jgt0 j--)
• if (arjgtarj1)
• temparj
• arjarj1
• arj1temp
• for (i0 ilt10 i)
• cout ltlt endl ltlt ari
• cout ltlt endl
• system("PAUSE")