Learn array in vb.net / PDF

Learn array in vb.net / PDF

1       OVERVIEW OF ARRAYS

The ability to work with arrays is important in any programming language. VB.NET offers a simple way of grouping data into the array structures similar to other languages.

1.1            Definition

Arrays are programming constructs that store data and allow us to access them by numeric index or subscript. All arrays in VB as zero based, meaning, the index of the first element is zero and they are numbered sequentially. Arrays have an upper bound and a lower bound, which simply refer to the starting index and the ending index of a given array structure.

1.2            Purpose of the Arrays

§  Arrays are generally used for storing similar types of values or objects. They allow grouping variables together and allow referring to them by using an index.

§  Arrays help us create shorter and simpler code in many situations.

§  Additionally, the data in the array can be sorted.

§  You can loop through an array to determine and to modify the values stored in the array.

1.3            Array Elements

What is an array element? When you define any type of array, you are actually defining a set of variables of the same data type that can be referenced by a single name. Each one of those item is called an element of the array. For instance in the following example: 1 is an element of the array arrNumbers().

Dim arrNumbers() As Integer arrNumbers = New Integer() {0,1,2,3,4}

1.4            Array Indexes

To distinguish one element of an array from the others, each element of an array is associated with an index number. That index number is used to reference each distinct element of the array. Note that the index must be positive.

1.5            Changing the Base Index of an Array

At times, starting an array with an index value of 0 (zero) seems counter-intuitive. For example, do users really think of January as zeroth month of the year, or do they think of it is the first month of the year? Generally speaking, January is considered as the first month of the year. Therefore, it would be nice to define the array in a way that is consistent with the way you expect to use the array. It would make more sense to have January have an index value of 1 than an index value of 0. There are several ways to accomplish this. Let’s use an example.

Dim sport(6) As String sport(0) = "Saturday" sport(1) = "Sunday" sport(2) = "Monday" sport(3) = "Tuesday" sport(4) = "Wednesday" sport(5) = "Thursday" sport(6) = "Friday"

One way to handle the above problem is to start by assigning nothing to the array at location 0, that is:

Dim sport(7) As String sport(0) = "" sport(1) = "Saturday" sport(2) = "Sunday" sport(3) = "Monday"

1.6            Array Dimension

An array can be one-dimension (linear arrays) or more than one (multidimensional arrays). The dimensionality of an array refers to the number of subscripts used to identify an individual element. 

1.7          Declaring Arrays

There are two ways of initializing the arrays: to declare and initialize them in one statement, or to declare an array and choose to initialize it later.

When declaring and initializing arrays in the same statement, you must specify the type of the array elements and the number of the elements the array will hold. You must specify the number of array elements by indicating the upper bound of the array; the upper bound is the number that specifies the index of the last element in the array. For instance, to declare & initialize an array of 5 integers, with indexes ranging from 0 to 4, we can write:

Dim arrNumbers(4) As Integer

Another way to declare and initialize arrays is to perform these operations in two separate steps. If you declare an array without specifying a number of elements on one line, you have to provide the values for each item of the array when you initialize it. The initial values are provided enclosed in the {} braces, using a comma as a separator.

To declare and initialize an array in two separate steps, we can write:

Dim arrNumbers() As Integer arrNumbers = New Integer() {0,1,2,3,4}

2       DEMONSTRATING ARRAYS USING EXAMPLE

Example 1:

               Create a form with one button so that if you click the button, the value stored in array ..

Learn array in vb.net / PDF