Arrays

1
Arrays

• Arrays are data structures consisting of data
  items of the same type.
• Arrays are static entities, in that they remain
  the same size once they are created
• MC provides manages arrays
• Managed arrays are actually objects of
  SystemArray class

2
Array

• Declaring and allocating arrays
• int c __gc
• // declare a managed array
• c new int __gc12
• // allocate space for array
• Arrays are allocated with new because arrays are
  objects and all objects must be created with new
• Managed types are garbage collected and managed
  by the CLR part of the .NET framework that
  executes MC program
• Managed arrays inherit from class SystemArray.

3

• double array1 __gc new double __gc10
• String b new String100,
• x new String27
• Double array new Double10
• Note that we do not have to include keyword __gc,
  because String represents a pointer to a
  managed type

4
Using array

• Every array in MC knows its own length.
• c-gtLength
• const int ARRAY_SIZE 10
• int z __gc
• z new int __gcARRAY_SIZE
• for( int i 0 i ltz-gtLength i)
• zi 2 2i
• for( int i 0 i lt ARRAY_SIZEi)
• ConsoleWrite(S0\t\t, zi.ToString())

5
Sorting Arrays

• Sorting data is one of the most important
  computing applications.
• Bubble sortuse nested loops to make several
  passes through the array. Each pass compares
  successive pairs of elements. If the pair is in
  decreasing order, the bubble sort swaps the
  values in the array
• ArraySort(a)

6
Bubble sort

• void bubblesort(int b __gc)
• int pass, I, hold
• for (pass 1 pass lt b-gtLength pass)
• for( I 0 I ltb-gtLength 1 I)
• if( bI gt bI1 )
• hold bI
• bI bI1
• bI1 hold

7
Searching arrays

• The process of locating a particular element
  value in an array is called searching
• Often, programmers work with large amount of data
  stored in arrays and often need to determine
  whether an array contains a value that matches a
  certain key value.
• Two searching techniques
• Simple linear search
• Binary search

8
Linear search

• Function linear search uses a for loop to compare
  each element to the key value. If the key is
  found, the function return the subscript of the
  element if the the search key is not found, the
  function return 1
• int linearsearch(int array __gc, int key)
• for (int I 0 I ltarray-gtLengthI)
• if( arrayI key) return I
• return 1

9
Binary search

• The linear search works well for small or
  unsorted array. However, for large arrays, linear
  searching is inefficient.
• Since arrays can be stored as sorted.
• High-speed binary search can be used on large
  sorted array

10
Binary search algorithm

• The algorithm locates the middle array element
  and compares it with the search key. If they are
  equal, the search key is found, and the subscript
  is returned otherwise, the problem is reduced to
  searching half of the array. If the key is less
  than the middle element, the first half of the
  array is searched otherwise, the second half of
  the array is searched. The search continues until
  the key is found or subarray consists one element
  that is not equal to the search key( the search
  key is not found)

11
Binarysearch function

• int BinarySearch(int array __gc, int key)
• int low0, higharray-gtLength-1, middle
• while( low lt high )
• middle (lowhigh)/2
• if( key arraymiddle ) return middle
• else if( key lt arraymiddle) high middle-1
• else low middle 1
• return 1

12
Practice

• Use a one-dimensional array to solve the
  following problem. A company pays its salespeople
  on a commission basis. The salespeople receive
  200 per week, plus 9 of their gross sales for
  that week. For example, a salesperson who grosses
  5000 in sales in a week receives 200 plus 9 of
  5000, or a total of 650. Write a program (using
  an array of counters) that determines how many of
  the salespeople earned salaries in each of the
  following ranges (assume that each salespersons
  salary is truncated to an integer amount)
• 200 299 300 399 400 499
• 500 599 600 699 700 799
• 800 899 900 999 1000 and over