Using textbox value in a loop

[dmroeder]

I did an experiment a while back for fun and I learned something about using text boxes in code (or any object for that matter).  The basic idea was to figure out what was in a password text box using brute force (one character at a time).  The reason I was doing this was because my wife had a really crappy password and I wanted to see how long it would take a processor to take to get a match by brute force.

It's a really silly experiment I know, and probably isn't the way that the real world works but I learned something that I thought was valuable (and probably common knowledge to real programmers):  Don't directly reference form objects in loops.  Read their state in code and use that variable instead (or at least in loops).  Here's what I mean:

Lets say the user is going to enter a single number and we wanted to use a loop to see when it is equal to 8:

Code: [Select]

'This way is slow
for i = 0 to 9
     if textbox1.text = (i) then  MessageBox.show("Success!")
next


Code: [Select]

'Faster
dim enteredValue as string = textbox1.text
for i = 0 to 9
     if enteredValue = (i) then MessageBox.Show("Success!")
next

Now a loop that is 0 to 9 isn't really significant but if you had a loop that requires many more operations, it can add up.  Here's an example.  In my test program, I entered 1234 into my password box and used some loops to increment characters one at a time until I got to the value.  1234 took 16,273,901 operations before I got to the value of 1234, which was 37.8 seconds.  In this example, I was comparing my incremented value directly to the text box (my first code example).  If I change the code to read the value of my textbox and store it in a variable (my second code example), then use the variable to do the compare, the time is cut to 1.9 seconds.

[Archie]

This is a really good way to demonstrate properties versus variables. When I teach someone object oriented programming for the first time, most people initially struggle with what a property really is. They appear and act so much like a variable that we can get stuck on thinking it is. In reality, a property contains two special kinds of function calls, the getter and the setter.

When you retrieve a property value, it calls the getter and executes some code to retrieve the value. It is typically just a single line of code, but can be as much code as needed. When you set the property to a value, it calls the setter function. More commonly the setter has more code because it can validate and even perform an action on the object.

Here is a typical property declaration that "maps" the property to an internal variable in the class:

Code: [Select]

    '* Internal private variable
    Private m_Value As Single

    '* Property declaration
    Public Property Value() As Single
        Get
            Return m_Value
        End Get

        Set(ByVal value As Single)
            If value <> m_Value Then
                '* Limit the value within the Min-Max range
                m_Value = Math.Max(Math.Min(value, 9999), -999)

                '*Invalidate to force a screen refresh
                Me.Invalidate()
            End If
        End Set
    End Property

You can see the "getter" retrieves what is stored in the variable m_Value and simply returns the value. However, the "setter" has a bit more code. It limits the value between -999 and 9999, then puts it into the variable m_Value.

So this is why directly referencing a property can be in efficient, especially in a large loop.