Getting started with BrainFuck

If ..., then do ..., else do ...

The second basic instruction in logic flow, after basic if ... then ...

Again, we want to end up at the same memory position whatever the path we choose.

Let's start

• Memory: A, 0
• Cursor: on A (condition to check)
• Input: any

Process

• set next cell to 1 (else flag)
• while A is not null
  • do something
  • while A is not null
    • decrease A
  • loop
  • A=0
  • reset else flag
• loop (but again A=0)
• go to else flag
• while flag is not null
  • do something else
  • reset else flag
• loop (but flag = 0)
• optionally, go back to A

Code

>+<        set next cell to 1 (else flag)
[          while A is not null
  ...      do something
  [-]      while A is not null decrease A
  >-<      reset else flag
]          loop (on an empty cell)
>          go to else flag
[          while flag is not null
  ...      do something else
  -        reset else flag
]          loop (on an empty cell)
<          optionall, go back to A

Minified version

>+<[...[-]>-<]>[...-]<

Final state

• Memory: 0
• Cursor: on 0
• Input: unchanged
• Output: unchanged

Test program

This code sample displays the char given in input 5 times, or "0" if nothing is provided

,              read input
>+<[           if not null
  .....        print value 5 times
[-]>-<]>[      else
  >++++++++    (6)
  [->++++++<]  (x8 = 48)
  >.           print (48 = '0' ASCII code)
  [-]<<        clean and back to original location
-]<