Transcript Document
Arrays
Arrays
A group of data with same type stored under
one variable.
It is assumed that elements in that group are
ordered in series.
In C# language arrays are has System.Array
type. So that they could use all functions of
System.Array class.
Arrays
As a simple example, think of days within a week.
This a one dimensional array whose first element is
monday and last element is sunday.
Another example is, the days within a month forms
2D (two dimensional) array. At horizontal there are
the days of week and at horizontal dimention there
are weeks.
We may think days of a year as a 3D array. 1st
dimension is days of week, 2nd dimension is week
and 3rd dimension is months.
Arrays
One dimensional array is defined with a
variable name, type and its length given
between square brackets.
Exaple,
int[] days = new int[ 7 ];
statement defines a one dimensional array
named days with seven elements.
Since this is a integer array, elements of it will
take initial value of zero.
Use of array
After defining array, we access its elements
with array name and index number within
square brackets, e.g. name_of_array[index]
In C# language first element in an array is at
index zero (0). Forexample, we can access at
least 0 and at most 6th index in days array
The numbers within square brackets are
called index numbers.
Index Numbers
int[] day = new int[7];
day[0] day[1] day[2] day[3] day[4] day[5] day[6]
2
6
6
4
Examples:
day[5] = 1;
if( day[5] == 4 ) break;
day[5] = day[6] - 1;
12
54
-10
Example
Variable i will
take values from
0 to 6 within for
loop
Initialization of arrays
As in the case of variables, we could also set
initial values to the arrays in the definition
phase.
static void Main(string[] args)
{
int[] day = { 0,2,4,6,8,10,11 };
..........
}
Initialization of arrays
static void Main(string[] args)
{
int[] day = { 0,2,4,6,8,10,11 };
}
Compiler counts the integer values and decides the value
in the[] brackets is 7 and compiles the program as
int[] gun = new int[7]
Initialization of arrays
If we are not assigning initial values to an array, then
elements of array will take initial values depending on
the type of the array.
For example numerical types will be zero and string
and other reference types will be “null”.
Warning:
Remember that a variable of type string having value of null null doesn’t
mean that it is an empty string. null means that there is no memory
allocated for that variable and its value can not be used in expressions yet.
Example
Define an array of double type that has 10 elements,
then assign values between 1.0 and 10.0. Finally swap
elements at 0 and 9 with each other.
static void Main(string[] args)
{
double[] arr = {1.0, 2.0, 3.0, 4.0,
5.0, 6.0, 7.0, 8.0,
9.0, 10.0};
double tmp;
tmp = arr[9];
arr[9] = arr[0];
arr[0] = tmp;
}
Exercise
Write a program that generates 100
random numbers and puts them to an
array.
Program should write smallest and
biggest numbers in the array to the
output. Also program should calculate
the mean value of the array and print it
to the output.
Exercise - Solution
The program below finds maximum and minimum values. Add calculation
of mean value feature to the program.
Array.Length()
Used in finding the length of the array.
Called right after the “.” mark after the
array name.
int[] myArray = new int[5];
int len = myArray.Length();
Console.WriteLine(len);
Output : 5
foreach Loop
This is a loop that iterates for each
element in a loop. It is forward only.
It look like for loop
foreach
foreach and for loops can be converted to
each other.
Multidimensional Arrays
These are arrays with more than one
dimension.
As an example we can use multidimensional
arrays for modeling a chess board.
Standard multidimensional
arrays
Creation of multidimensional arrays are similar to one
dimensional ones. The difference is there is a comma
between the square brackets.
int [,] numbers;
string [,,] lines;
As an example, a string type two by three
multidimensional array can be created with
string[,] array = new string[2,3];
Standard multidimensional
arrays
All dimension lengths are equal in standard arrays. Therefore they look like
matrices.
array
1
2
3
9
20
5
2
4
0
6
7
0
4
2
11
Standard multidimensional
arrays
Lets create a 2D multidimensional array and assign values to its
elements in a loop.
Array operations
Searching and sorting
Array Operations
Some of the most used array functions
in programming;
IndexOf()
LastIndexOf()
Sort()
Reverse()
They are defined within Array class.
IndexOf() - LastIndexOf()
IndexOf() : Starts searching from first
element and returns the index number
of element found.
LastIndexOf() : Starts searching from
last element and returns the index
number of element found.
If the element that we are looking for is
not in the list, that these function return
-1.
Array.IndexOf(), Array.LastIndexOf()
Result : 1
Result : 4
Array.Sort()
Sorts the elements of the array by ascending order.
Result :
Ali
Mehmet
Pınar
Zeynep
Array.Reverse()
Reverses the order of the elements of the array.
Result :
45
32
9
5
3
2
1
Not : Array.Sort and Array.Reverse
does not have to be used together.
Problem
If we don’t know the size of the array in
advance?
What if array expands dynamically?
Collections
Used in situations of which the length
of the array is not known in advance.
Or the length of the array grows or
shrinks dynamically.
They are one dimensional.
ArrayList
It is one of the basic collection types.
Resides in System.Collections
namespace.
It has initial length of 16 and for each
expansion, its length is multiplied by 2.
Stores data as type of object.
ArrayList
Creating a new ArrayList:
ArrayList list = new ArrayList();
Example
ArrayList
Important functions and properties
Add
Capacity
Clear
Count
IndexOf
Insert
RemoveAt
Reverse
Sort
TrimToSize
Exercise
Define an ArrayList to hold the names of staff.
Add the names; Ahmet, Mehmet, Pınar, Yeşim,
Utku, Sinan, Fatma, Ayşe to the list.
Print the list and its size to output.
Delete the elements which are stating with
letter ‘A’ from the list
Sort the list with reverse order.
Print the list and its size to output.
Exercise
Solution