The Times Table Code

 

As you can see from our last lesson, we've set up five Integer variables - number1, number2, multiplier, answer and i.

The next thing we did was to pass whatever is in our two Textboxes straight into the two variable, number1 and number2. The start number goes into textbox one, and the end number goes into textbox2.

number1 = Val(TextBox1.Text)
number2 = Val(TextBox2.Text)

In the next line of code, we set a starting value for the multiplier variable:

multiplier = 2

Then we had our two Loops, one inside the other. The first is the Do Loop:

Do While multiplier < 3

multiplier = multiplier + 1

Loop

This Do loop is exactly the same as the one you met before. All is does is go round and round While the variable called multiplier is Less Than 3. The bit of code between Do and Loop just keeps adding one to whatever is in multiplier (incrementing the variable).

The other thing the Do Loop does is to execute our second loop - the For Loop. The For Loop gets executed each time around the Do Loop. The For Loop was this:

For i = number1 To number2

answer = i * multiplier
ListBox1.Items.Add(i & " Times " & multiplier & " = " & answer)

Next i

Remember: the number1 and number2 variables hold our numbers from the Textboxes. We set these to 1 and 10. So our first line of the For Loop is really this:

For i = 1 To 10

We're saying, "Start a For Loop". Whatever is in the variable called number1, make that the starting number for the Loop. Put this value into the variable called i. The end of the Loop will come when the variable called i has the value 10. Stop looping when you reach this value.

The next part of the code reads this:

answer = i * multiplier

This means, Put into the variable called answer the following sum: whatever is in the variable called i multiplied by whatever is in the variable called multiplier.

(For a longer discussion on how to use the basic Maths symbols in VB .NET, see here: basic Maths symbols in VB .NET )

So that says, put into the variable answer the sum of i times multiplier. We're getting whatever is in i from the For loop. But we're getting whatever is in the variable called multiplier from the Do Loop.

So Visual Basic will read the Do While line after noting that the number 2 has been put into the variable called multiplier. It will then check to see if the end of the loop condition has been met - multiplier is Less Than 3. As 2 is not Less Than 2, VB drops down to the next line.

The next line is a For Loop - For i = 1 To 10. This entire loop will be executed, and the code inside the For loop worked out.

So the For loop gets executed 10 times. Which means that our sum will get executed 10 times. When the end condition of the For loop is met, Visual Basic will exit the For Loop and drop down to the line of code below Next i. The code below Next i is this:

multiplier = multiplier + 1

What was inside the variable called multiplier was the number 2, so 2 + 1 = 3. And three is the new number inside the variable multiplier.

Then, Visual Basic drops down to the next line, which is Loop. So it goes back up to the Do While line of code

Do While multiplier < 3

The same question is asked again: Have we met the end condition for the Do Loop? The end condition was "Keep looping while the variable called multiplier is Less Than 3".

Because the value in multiplier is now equal to 3 and not less than 3, the end condition has been met. When the end condition is met, VB exists the Do loop.

 

No more reading these lessons online - get the eBook here!

 

Finally, a word about the line that displays your text in the list box. It was this:

ListBox1.Items.Add(i & " Times " & multiplier & " = " & answer)

To add items to a list box with code, first you type the name of your list box:

ListBox1

Type a full stop and a drop down list will appear. Select Items from the list.

ListBox1.Items

Type another full stop and again a drop down list will appear. Select the Add Method

ListBox1.Items.Add

This method, not surprisingly, lets you add items to your list box. Whatever you want to add goes between a pair of round brackets:

ListBox1.Items.Add( )

In between the round brackets, we have this for our code:

i & " Times " & multiplier & " = " & answer

It might be a bit long, but there are 5 parts to it, all joined together by the concatenate symbol (&):

i
" Times "
multiplier
" = "
answer

The variable i holds the current value of the For Loop; " Times " is just direct text; multiplier holds the value we're multiplying by (our times table); " = " is again direct text; and answer is the answer to our times table sum.

If you want to clear the items from a List box you can do this. At the top of the code, enter this line:

ListBox1.Items.Clear()

So instead of selecting Add from the final drop down list, select Clear.

In the next part, we'll take a closer look at the basic Maths symbols you can use in VB .NET.

 

Click here to move on to the basic Maths symbols in VB .NET-->

<--Back to the .NET Contents Page

View all our Home Study Computer Courses