Wyo VB Lecture Notes

Objective #1: Generate random numbers within desired ranges using the Rnd method.

• Technically, it is impossible to generate a truly random number with a computer since it does not have a mind of its own to pick numbers at random. The number that the computer generates must be based on something else such as the number of seconds since midnight. Therefore it is best to describe these numbers as pseudorandom rather than truly random.
  
  
• You can use the built-in method Rnd to generate random numbers. The Rnd method generates and returns a decimal number between 0 and 0.9999.
  
  Examples:
  MessageBox.Show(Rnd()) ' 0.345 could be displayed
  MessageBox.Show(Rnd()) ' 0.891 could be displayed
  MessageBox.Show(Rnd()) ' 0.003 could be displayed
  MessageBox.Show(Rnd()) ' 0.999 could be displayed
  
  
• Typically, you want an integer to be generated as a random number rather than a decimal number. Here's an algorithm for turning the decimal number that Rnd generates into an integer. The following examples show how you can simulate the roll of a regular 6-sided dice with the Rnd method:
  
  - multiply the value that Rnd generates by 6
  - chop off the decimal places
  - add 1
  
  Study the following examples to see the algorithm in action:
  
  Dim num As Double = 0
  num = Rnd()                   ' 0.000 is the smallest possible pseudorandom number that Rnd generates
  MessageBox.Show(num)          ' 0.000
  num = num * 6                 ' num is now 0.000 since 0.000 * 6 = 0.000
  MessageBox.Show(num)          ' 0.000
  num = Math.Floor(num)         ' the decimal places in 0.000 are truncated and "cut off"
  MessageBox.Show(num)          ' 0
  num = num + 1                 ' 1 is added since a dice typically displays the numbers 1 through 6 not 0 through 5
  MessageBox.Show(num)          ' 1 is the dice roll
  
  Dim num As Double = 0
  num = Rnd()                   ' 0.001 could be a pseudorandom number that Rnd generates
  MessageBox.Show(num)          ' 0.001
  num = num * 6                 ' num is now 0.006 since 0.001 * 6 = 0.006
  MessageBox.Show(num)          ' 0.006
  num = Math.Floor(num)         ' the decimal places in 0.006 are truncated and "cut off"
  MessageBox.Show(num)          ' 0
  num = num + 1                 ' 1 is added since a dice typically displays the numbers 1 through 6 not 0 through 5
  MessageBox.Show(num)          ' 1 is the dice roll
  
  Dim num As Double = 0
  num = Rnd()                   ' 0.555 is a number near the middle of the range of possible pseudorandom numbers that Rnd generates
  MessageBox.Show(num)          ' 0.555
  num = num * 6                 ' num is now 3.33 since 0.555 * 6 = 3.33
  MessageBox.Show(num)          ' 3.33
  num = Math.Floor(num)         ' the decimal places in 3.33 are truncated and "cut off"
  MessageBox.Show(num)          ' 3
  num = num + 1                 ' 1 is added since a dice typically displays the numbers 1 through 6 not 0 through 5
  MessageBox.Show(num)          ' 4 is the dice roll
  
  Dim num As Double = 0
  num = Rnd()                   ' 0.999 is the largest possible pseudorandom number that Rnd can generate
  MessageBox.Show(num)          ' 0.999
  num = num * 6                 ' num is now 5.994 since 0.999 * 6 = 5.994
  MessageBox.Show(num)          ' 5.994
  num = Math.Floor(num)         ' the decimal places in 5 are truncated and "cut off"
  MessageBox.Show(num)          ' 5
  num = num + 1                 ' 1 is added since a dice typically displays the numbers 1 through 6 not 0 through 5
  MessageBox.Show(num)          ' 6 is the dice roll
  
  
• The formula      Math.Floor(Rnd() * (High - Low + 1)) + Low
  
  can be used to generate a random whole number between and including the values substituted for Low and High
  
  For example, if you want to generate a random number between 1 and 6 then you plug 1 in for Low in the formula above and you plug in 6 for High
  
  diceRoll = Math.Floor(Rnd() * (6 - 1 + 1)) + 1   which simplies to ....
  diceRoll = Math.Floor(Rnd() * (5 + 1)) + 1                     which simplies to ....
  diceRoll = Math.Floor(Rnd() * 6) + 1
  
  Or, if you want to generate a random number between 10 and 20 then you plug 10 in for Low you plug in 20 for High
  
  
  diceRoll = Math.Floor(Rnd() * (20 - 10 + 1)) + 10      which simplies to ....
  diceRoll = Math.Floor(Rnd() * (10 + 1)) + 10                       which simplies to ....
  diceRoll = Math.Floor(Rnd() * 11) + 10
  
  
• The statement
  
  Dim probability As Double = 0.0
  probability = Rnd()
  
  would store a random decimal number between 0 and 0.99999 into the variable probability. So the If statement
  
  If (probability < 0.5) Then
     MessageBox.Show("Heads")
  Else
     MessageBox.Show("Tails")
  End If
  
  simulates the flip of a coin.
  
  Or, you could use the following If statement to simulate a baseball player's at bat where he/she has a 1/3 chance of getting a hit, a 1/3 chance of striking out, and a 1/3 chance of getting a walk to first base
  
  If (probability < 0.333) Then
     MessageBox.Show("The baseball player gets a base hit.")
  ElseIf (probability < 0.666) Then
     MessageBox.Show("The baseball player strikes out")
  Else
     MessageBox.Show("The baseball player gets a walk to first base.")
  End If
  
  
• Use the Randomize statement first though in the Form1_Load method. This "seeds" the VB random number generator so that your program doesn't generate the same pattern of random numbers every time it runs.

Objective #2: Use random numbers to simulate dice rolls and computer interactions with a player in a game.

• In some games, you roll one dice. So you may end up using the code segment
  
  Private Sub btnRoll_Click(...)
     Dim diceRoll As Integer = 0
  
     diceRoll = Math.Floor(Rnd() * 6) + 1
  
     MessageBox.Show(diceRoll)
  End Sub
  
  If you need to roll two dice, then you might use code like this
  
  Private Sub btnRoll_Click(...)
     Dim diceRoll1 As Integer = 0
     Dim diceRoll2 As Integer = 0
     Dim total As Integer = 0
  
     diceRoll1 = Math.Floor(Rnd() * 6) + 1
     diceRoll2 = Math.Floor(Rnd() * 6) + 1
  
     total = diceRoll1 + diceRoll2
  
     MessageBox.Show(total)
  End Sub
  
  If you need to simulate a baseball player's turn at bat, you might use something like this
  
  Private Sub btnAtBat_Click(...)
     Dim batterAction As Integer = 0
  
     batterAction = Rnd()
  
     If (batterAction < .200) Then
        MessageBox.Show("single")
     ElseIf (batterAction < .300) Then
        MessageBox.Show("double")
     ElseIf (batterAction < .320) Then
        MessageBox.Show("triple")
     ElseIf (batterAction < .350) Then
        MessageBox.Show("home run")
     ElseIf (batterAction < .500) Then
        MessageBox.Show("walk")
     ElseIf (batterAction < .750) Then
        MessageBox.Show("grounded out or pop fly out")
     Else
        MessageBox.Show("strikeout")
     End If
  
  End Sub