tutorial

turtles-own [energy]

to go
  if ticks >= 500 [ stop ]
  move-turtles
  eat-grass
  reproduce
  check-death
  regrow-grass
  tick
end 

to move-turtles
  ask turtles [
    right random 45
    left random 45
    forward 1
    set energy energy - 1
  ]
end 

to setup
  clear-all
  setup-patches
  setup-turtles
  reset-ticks
end 

to setup-patches
  ask patches [ set pcolor green ]
end 

to setup-turtles
  create-turtles number [ setxy random-xcor random-ycor ]
end 

To eat-grass
  ask turtles [
    if pcolor = green [
      set pcolor black
      set energy (energy + energy-from-grass)
    ]
    ifelse show-energy?
      [ set label energy ]
    [ set label " " ]
  ]
end 

to reproduce
  ask turtles [
    if energy > 50 [
      set energy energy - 50
      hatch 1 [ set energy 50 ]
    ]
  ]
end 

to check-death
  ask turtles [
    if energy <= 0 [ die ]
  ]
end 

to regrow-grass
  ask patches [
    if random 100 < 3 [set pcolor green ]
  ]
end