Vbscript basic functions

Question

I am new to programming and computer science. HTML is all I know and I have been facing problems with vbscript. This program (my first in vbscript) was given by my teacher. But I really do not understand anything. I referred to my book but in vain. I am not even sure if this is the right SE to post the question. Please help.

Answer 1

What you have there is a loop with another nested loop, both of which print some text to the screen (document.write("...")).

The outer loop

For i = 1 To 5 Step 1
  ...
Next

iterates from 1 to 5 in steps of 1 (which is redundant, since 1 is the default step size, so you could just omit the Step 1). If you printed the value of i inside the loop

For i = 1 To 5 Step 1
  document.Write(i & "<br>")
Next

You'd get the following output:

1
2
3
4
5

In your code sample you just print <br>, though, so each cycle of the outer loop just prints a line break.

In addition to printing line breaks in the outer loop you also have a nested loop, which for each cycle of the outer loop iterates from 1 to the current value of i, again in steps of 1.

For j = 1 To i Step 1
  ...
Next

So in the first cycle of the outer loop (i=1) the inner loop iterates from 1 to 1, in the second cycle of the outer loop (i=2) it iterates from 1 to 2, and so on.

For i = 1 To 5 Step 1
  document.Write(i & "<br>")
  For j = 1 To i Step 1
    document.Write("*")
  Next
Next

Since the inner loop prints an asterisk with each cycle you get i asterisks per line before the inner loop ends, the outer loop then goes into the next cycle and prints a line break, thus ending the current output line.

A good (although somewhat tedious) way to get an understanding of how the loops work is to note the current value of each variable as well as the current output line in a table on a sheet of paper, e.g. like this:

code line | instruction            |   i   |   j   | output line
----------+------------------------+-------+-------+------------
        1 | For i = 1 To 5 Step 1  |   1   | Empty |
        2 | document.Write("<br>") |   1   | Empty | <br>
        3 | For j = 1 To i Step 1  |   1   |   1   |
        4 | document.Write("*")    |   1   |   1   | *
        5 | Next                   |   1   |   1   | *
        6 | Next                   |   1   |   1   | *
        1 | For i = 1 To 5 Step 1  |   2   |   1   | *
        2 | document.Write("<br>") |   2   |   1   | *<br>
        3 | For j = 1 To i Step 1  |   2   |   1   | 
        4 | document.Write("*")    |   2   |   1   | *
        5 | Next                   |   2   |   1   | *
        3 | For j = 1 To i Step 1  |   2   |   2   | *
        4 | document.Write("*")    |   2   |   2   | **
        5 | Next                   |   2   |   2   | **
        6 | Next                   |   2   |   2   | **
        1 | For i = 1 To 5 Step 1  |   3   |   2   | **
        2 | document.Write("<br>") |   3   |   2   | **<br>
        3 | For j = 1 To i Step 1  |   3   |   1   | 
        4 | document.Write("*")    |   3   |   1   | *
      ... | ...                    |  ...  |  ...  | ...