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 returns a decimal number between 0 and 1. Actually, the random number could be 0 exactly but it will not be 1 exactly.
  
  
• Using the statement
  
  intDiceRoll = Math.Floor(Rnd() * (Hi - Lo + 1)) + Lo
  
  you can generate a random whole number between and including the values substituted for Lo and Hi and store that random number in the variable intDiceRoll.
  
  
• Use the Randomize statement first though in the Form_Load method. This "seeds" the VB random number generator so that your program doesn't generate the same random numbers every time it executes.
  
  
• The statement
  
  dblProbability = Rnd()
  
  would generate a random decimal number between 0 and 1 (but not including 1). So you could follow this with an If statement such as
  
  If (dblProbability < 0.5) Then
     MessageBox.Show("It is going to snow")
  Else
     MessageBox.Show("It is NOT going to snow")
  End If
  
  to simulate a 50% chance of snow.
  
  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 (dblProbability < 0.333) Then
     MessageBox.Show("The baseball player gets a base hit.")
  ElseIf (dblProbability < 0.666) Then
     MessageBox.Show("The baseball player strikes out")
  Else
     MessageBox.Show("The baseball player gets a walk to first base.")
  End If
  
  
• Using the formula without that Math.Floor method can be used to generate a decimal number within a larger range such as between 1 and 100 (but not including the 100) as in
  
  dblProbability = Rnd() * (Hi - Lo + 1) + Lo
  which simplifies to
  dblProbability = Rnd() * (100 - 1 + 1) + 1
  and simplifies further to
  dblProbability = Rnd() * 100 + 1
  

Objective #2: Generate random numbers within desired ranges using Random.

• There is another way in which random numbers can be produced however this method will not be tested on worksheets or exams in this Visual Basic course. You can use the built-in VB class named Random to generate random numbers.
  
  
• The statement
  
  Dim dice As New Random
  
  declares a Random object named dice. I don't require that you use a specified prefix when naming Random objects.
  
• The Next method returns an integer number between 0 and one less than its parameter. For example, the statement
  
  MessageBox.Show(dice.Next(6))
  
  displays a pseudorandom integer between or including 0 and 5. If you want to simulate the roll of a dice, then you must add one to the the value that is returned by the Next method as in
  
  MessageBox.Show(dice.Next(6) + 1)
  
• To seed the Random object, you use the following statement to declare the Random object.
  
  Dim dice As New Random(1)
  
  with some integer seed value specified in the parentheses. Any number will work fine. The result will be that the string of random values generated by the Next method will be the same pattern of random values. This is helpful when testing and debugging a program.
  
• Use the nextDouble method to generate a pseudorandom floating-point value. The following statement will display a random decimal number between 0 inclusive and 1 exclusive meaning that 0 could be a returned value but 1 will not be a possible returned value.
  
  MessageBox.Show(dice.NextDouble())