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Small Basic - Random Numbers

  • Artigo

Random numbers can be very useful in your Small Basic games.  They can be used to make the game play vary from one game to the next.

The Small Basic keyword to get a random number is Math.GetRandomNumber(maxNumber) .  It will return a random integer between 1 and the input value maxNumber.

Here are a few ideas and tips:

Random Position and Speed

We can position sprites with random positions and velocities.

radius `` = ``25

numSprite `` = ``10

gw `` = ``GraphicsWindow``.``Width

gh `` = ``GraphicsWindow``.``Height

For `` i `` = `` 1 `` To ``numSprite

  ``sprite``[``i`` ] `` = ``Shapes``.``AddEllipse``(``2``*``radius``,``2``*``radius``)

  ``spritePosX``[``i`` ] `` = ``radius``+``Math``.``GetRandomNumber``(``gw``-``2``*``radius``)

  ``spritePosY``[``i`` ] `` = ``radius``+``Math``.``GetRandomNumber``(``gh``-``2``*``radius``)

  ``spriteVelX``[``i`` ] `` = ``Math``.``GetRandomNumber``(``11``)``-``6

  ``spriteVelY``[``i`` ] `` = ``Math``.``GetRandomNumber``(``11``)``-``6

EndFor

 

While ``"True"

  `` For `` i `` = `` 1 `` To ``numSprite

    ``spritePosX``[``i`` ] `` = ``spritePosX``[``i``]``+``spriteVelX``[``i``]

    ``spritePosY``[``i`` ] `` = ``spritePosY``[``i``]``+``spriteVelY``[``i``]

    `` If ``(``spritePosX``[``i`` ] `` < ``radius`` ) ``Then

      ``spritePosX``[``i`` ] `` = ``radius

      ``spriteVelX``[``i`` ] `` = ``-``spriteVelX``[``i``]

    `` ElseIf ``(``spritePosX``[``i`` ] `` > ``gw``-``radius`` ) ``Then

      ``spritePosX``[``i`` ] `` = ``gw``-``radius

      ``spriteVelX``[``i`` ] `` = ``-``spriteVelX``[``i``]

    ``EndIf

    `` If ``(``spritePosY``[``i`` ] `` < ``radius`` ) ``Then

      ``spritePosY``[``i`` ] `` = ``radius

      ``spriteVelY``[``i`` ] `` = ``-``spriteVelY``[``i``]

    `` ElseIf ``(``spritePosY``[``i`` ] `` > ``gh``-``radius`` ) ``Then

      ``spritePosY``[``i`` ] `` = ``gh``-``radius

      ``spriteVelY``[``i`` ] `` = ``-``spriteVelY``[``i``]

    ``EndIf

    ``Shapes``.``Move``(``sprite``[``i``]``,``spritePosX``[``i``]``-``radius``,``spritePosY``[``i``]``-``radius``)

  ``EndFor

  ``Program``.``Delay``(``20``)

EndWhile

Random Branching

We can randomly do different things in the code,  perhaps equivalent to rolling a dice.

dice `` = ``Math``.``GetRandomNumber``(``6``)

If ``(`` dice `` = ``1`` ) ``Then

  ``TextWindow``.``WriteLine``(``"Do something for a dice roll of 1"``)

ElseIf ``(`` dice `` = ``2`` ) ``Then

  ``TextWindow``.``WriteLine``(``"Do something for a dice roll of 2"``)

ElseIf ``(`` dice `` = ``3`` ) ``Then

  ``TextWindow``.``WriteLine``(``"Do something for a dice roll of 3"``)

ElseIf ``(`` dice `` = ``4`` ) ``Then

  ``TextWindow``.``WriteLine``(``"Do something for a dice roll of 4"``)

ElseIf ``(`` dice `` = ``5`` ) ``Then

  ``TextWindow``.``WriteLine``(``"Do something for a dice roll of 5"``)

ElseIf ``(`` dice `` = ``6`` ) ``Then

  ``TextWindow``.``WriteLine``(``"Do something for a dice roll of 6"``)

EndIf

We could also only do something with a probability, say 1 in 10.

If ``(``Math``.``GetRandomNumber``(``10`` ) `` = ``1`` ) ``Then

  ``TextWindow``.``WriteLine``(``"This is a 1 in 10 event!!!"``)

Else

  ``TextWindow``.``WriteLine``(``"A 10% probability event didn't happen"``)

EndIf

Ranges and Intervals

If we want random numbers over a different range (not 1 to maxNumber) or with smaller intervals, for example 0.2, then we can use the following formula.

rand `` = `` min `` + ``(``Math``.``GetRandomNumber``(``1``+``(``max``-``min``)``/``interval``)``-``1``)``*``interval

Here is an example using this to create random numbers between -5 and 3, with intervals of 0.2.

min `` = ``-``5

max `` = ``3

interval `` = ``0.2

For `` i `` = `` 1 `` To ``1000

  ``Random``(``)

  ``TextWindow``.``WriteLine``(``rand``)

EndFor

Sub ``Random

  `` rand `` = `` min `` + ``(``Math``.``GetRandomNumber``(``1``+``(``max``-``min``)``/``interval``)``-``1``)``*``interval

EndSub

 

Comments

  • Anonymous
    July 13, 2014
    Hey I wonder if we can do a community project around random numbers. This is cool, thanks for explaining this, LitDev!

  • Anonymous
    July 15, 2014
    LitDev, I think there is a slight error in your formula.  It generates a random number from min+interval to max+1. You can see in the image that it generates 4.0 when the max is set at 3. If you remove the +1 from the formula then it gets rid of the max+1 error, but I'm not sure how to get it to generate the min as the lowest number.

  • Anonymous
    July 16, 2014
    Ozjerry - Excellent catch, Does this look right to you. Sub Random  rand = min + (Math.GetRandomNumber(1+(max-min)/interval)-1)*interval EndSub

  • Anonymous
    July 16, 2014
    LitDev - Works perfectly.  I ran it through a 10,000 iterations at varying min/max values at it's perfect every time. I tried to fix it myself prior to posting, but just couldn't get it to hit both the min and max values.  I figured it was something to do with the fact that GetRandomNumber doesn't generate a zero, but I couldn't figure out the workaround.  So kudos to you for working it out. Thanks

  • Anonymous
    July 19, 2014
    I have corrected the original post - Thanks again Ozjerry.

  • Anonymous
    July 22, 2014
    The comment has been removed