BrainFuck part 10 - RPN calc tool


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Read integers

Let's define what we want to read first

  • Digits (0 to 9, codes from 48 to 57)
  • Space (separator, code 32)

Our program will read numbers, space separated, and push them onto the stack

Let's start

  • Memory: empty
  • Cursor: first cell
  • Input: space separated integers


  • Leave an empty space (current number on stack is null)
  • While there is a char to read
    • subtract 32 and set else flag
    • if char is null : it's space
      • reset else flag, move to the right
    • otherwise
      • subtract 16 (to get the digit value)
      • add current number 10 times to current digit to get new current number
  • loop


>,[                     leave empty space and read char
  let's track our target values here
  space 32
  digit 48 to 57

  >++++[-<-------->]+<  subtract 32
  [                     it's a digit
    >+++[-<---->]<      subtract 16 (total 48)
    <[->++++++++++<]    add current number 10 times to current digit
    >[-<+>]             replace current number by current digit
  ]>[-                  it's space
    >                   move to next stack entry
  ]                     end of switch/case
<,]                     read char and loop

Final state

  • Memory: stack of integers
  • Cursor: after stack
  • Input: empty (read)
  • Output: unchanged

Test program

This program reads space-separated integers and then print them all as chars

>                         leave an empty cell (to go back to stack start)
>,[>++++[-<-------->]+<[  calc tool code
>+++[-<---->]<<[->++++++    ** part 2 **
++++<]>[-<+>]]>[->]<,]      ** part 3 **
<[<]>[.>]                 go back to the stack first cell and print whole stack as char
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