Getting started with BrainFuck

DPAmar
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Subtract numbers

Like we did for addition : in order to compute A-B, we have to subtract 1 to A, B times

Let's start

  • Memory: A, B
  • Cursor: on B
  • Input: any

Process

  • while B is not null
    • invariant: A cell - B cell = A-B
    • decrease B
    • increase A
  • loop
  • B cell = 0, A cell = A-B - 0 = A-B

Code

[    while B is not null
  -  decrease B
  <- go to A and increase
  >  go back to B
]    loop

Minified version

[-<->]

Final state

  • Memory: A-B, 0
  • Cursor: "0" cell
  • Input: unchanged
  • Output: unchanged
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