We use arrays every
day
A pack of M&Ms is a
great example of an array. It’s easy for us to imagine a bag of this popular
candy. We can imagine each one of the M&Ms as they are taken from the bag.
They are all basically the same but different colors. Even though they are
different colors, they are all chocolate candy with a hard candy A bag of
M&M's is an array of datatype M&M's. It is a collection of
candy.
How do I declare an
array?
Declaring an array is very
much like declaring other variables. The only difference is that you are
declaring a variable that will hold more than one object. Let’s compare these
two declarations.
String strEmotion = “happy”;
String[] strEmotions =
{“happy”,”sad”,”elated”,”afraid”,”angry”,”peaceful”};
Both of the variables
above, strEmotion and strEmotions, have been declared using Explicit Declaration
which means the value is set at the same time they are created.
By using
the brackets [] , the compiler knows that the variable strEmotions will hold
more than one value. The number of items and the values is set with =
{“happy”,”sad”,”elated”,”afraid”,”angry”,”peaceful”}; In this case, we have set
the size of the array to 6 because we have added 6 values.
Now we take a closer look
at these 2 variable declarations…
|
Variable
Name |
Datatype |
Number of
Value(s) |
Value(s) |
|
strEmotion |
String |
1 |
happy |
|
strEmotions |
String |
6 |
happy, sad, elated,
afraid, angry, peaceful |
How do I get a
specific value?
Getting the value of each item isn’t hard once you
understand how the array refers to each item. At first it might be a little
confusing because arrays use a zero based reference. This means
that the first item in the list is in the 0 position. Huh? Okay, look at
the next lines and you’ll understand.
String [] strEmotions =
{“happy”,”sad”,”elated”,”afraid”,”angry”,”peaceful”};
|
strEmotions[0] =
happy |
Value in the 0 positon of the
array |
|
strEmotions[1] =
sad |
Value in the 1 position of the
array |
|
strEmotions[2] =
elated |
Value in the 2 position of the
array |
|
strEmotions[3] = afraid
|
Value in the 3 position of the
array |
|
strEmotions[4] =
angry |
Value in the 4 position of the
array |
|
strEmotions[5] =
peaceful |
Value in the 5 position of the
array |
Putting it all to work
In this example, we have
an array of data type System.Drawing.Colors that we will use to change the
background color of a form. This very simple application will help in
understanding how to reference each of the different items in an array. It also
shows how to find out which control called the function.
Let’s
look at each line…
First
an array of data type System.Drawing.Color is declared and four colors, Gree,
Red, Yellow, and Blue are added at the same time. Notice the brackets [] which
signify an array declaration. Because we populate the array at the time we
declare it, we say that it was explicitly declared.
System.Drawing.Color[] myColorArray = {System.Drawing.Color.Green,
System.Drawing.Color.Red , System.Drawing.Color.Yellow, System.Drawing.Color.Blue};
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|
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Now we add a method and assign it to the click event of
all the radio buttons. We could have written this under four different methods,
one for each of the radio buttons. But since they are almost identical, it’s
better to add them in one method and then find out which radio button called it.
This also makes it much easier to support later on down the road (One Method
rather than Four Methods).
private void
ChangeColors(object sender, EventArgs e)
{
/*Get a reference to the radio
button that called the function. We know that the control that is going to call
this method will be a Radio Button so first we create a variable of datatype
Radio Button. Then we set our variable = to the sender object. But we need first
to convert the sender variable to a datatype of Radio*/
System.Windows.Forms.RadioButton rbtn = (System.Windows.Forms.RadioButton)sender;
Next find out which radio button it was by
finding the name of the button.
if (rbtn.Name ==
"rbtnGreen")
this.BackColor = myColorArray[0];// <---first item is the array is in the 0
position
if (rbtn.Name == "rbtnRed")
this.BackColor =
myColorArray[1];// <---second item is the array is
in the 1st position
if (rbtn.Name ==
"rbtnYellow")
this.BackColor = myColorArray[2];// <---third item is the array is in the 2nd
position
if (rbtn.Name == "rbtnBlue")
this.BackColor =
myColorArray[3];// <---fourth item is the array is
in the 3rd position
}
Download the sample code to see how this code works to
change the back color of a windows form.
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