How to deplete a global variable?

I need a little guidance on how to completely use a global variable.

I have the global variable num-tourists which is a number of how many tourists come to a place.

Then, I have my turtles get the maximum number of tourists (15), and they charge them 100,000. Each of my sellers can handle up to 15 tourists.

ask turtles with [turism = 1]
      [set earnings (earnings + ((15) * 100000))]
[set num-tourists num-tourists - 15]

However, I don't know how to tell the code that, if there is less than 15, it can take whatever is left, then multiply that by 100000

Solution

This is similar to the "Move Towards Target Example" in the NetLogo library. Functionally, you want to: count the number of remaining tourists. If that number is higher than 15, multiply 10000 X 15. Otherwise, multiply 10000 X (n remaining tourists). Here is one way:

globals [num-tourists total-earnings]

to setup
  ca
  set num-tourists 40
  set total-earnings 0
  print (word "There are " num-tourists " tourists")
  reset-ticks
end

to go
  ifelse num-tourists > 15 [
    set total-earnings total-earnings + (15 * 10000)
    set num-tourists num-tourists - 15
  ] [
    set total-earnings total-earnings + (num-tourists * 10000)
    set num-tourists num-tourists - num-tourists
    ; equivalently, set num-tourists 0
  ]
  print (word "There are " num-tourists " tourists, and the total earnings are " total-earnings)  
  tick
end