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Simple programming training puzzle (repeat)

  1. Dec 17, 2011 #1


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    This is a repost of an old thread, maybe some new members can give it a shot. This puzzle was included at the start of a casual IBM Fortran programming class for high school students back in 1969. (Yes, I'm that old). I don't know the origin of this puzzle.

    An extremely simple and old (1960's) programming language based on an imaginary machine. The machine has two peripherals, at paper tape reader, and a paper tape punch. The character set only includes two characters, Asterisk and Hypen. The CPU has 20 memory locations, which hold instructions, but only the first 10 locations, 0 through 9 are addressable via the branch instruction.

    There are only 13 instructions, and 4 basic types of instruction:

    T - Read a character from the tape reader. If the character read is a hyphen, execute next instruction. If the character read is an asterisk, skip the next instruction, and execute the instruction following the next instruction. If no character is read because the paper tape is past the end, then the machine will stop.

    H - Punch a hypen, then execute next instruction.

    A - Punch an asterisk, then execute next instruction.

    0 - branch to location 0 and continue execution there.
    1 - branch to location 1 and continue execution there.
    2 - branch to location 2 and continue execution there.
    9 - branch to location 9 and continue execution there.

    Instruction execution can continue past memory location 9, but these memory locations can't be the target of a branch instruction.

    Programming tasks:

    1. Write a program to duplicate the paper tape in the reader using the paper tape punch.

    2. Write a program to read the paper tape until 3 asterisks in a row are read, then start duplicating the paper tape as in program 1.

    3. Write a program to read the paper tape until 3 asterisks in a row are read, then start duplicating the paper tape, but stop all I/O once 3 asterisks in a row are punched during the copy process.

    Note that since there are only 13 instructions, trial and error will be good enough to write any of these programs.

    To avoid spoilers, please white out your repsonse using
    tags , or merely indicate that you've solved how to create programs 1, 2, and/or 3.

    Example of a failed attempt at a copy program:

    Code (Text):

    0 1 2 3 4 5 6 7 8 9 X X X X X X X X X X
    T H A 0
    This program will punch a hyphen and asterisk for every hyphen read, and punch an asterisk for every asterisk read. It's a broken copy program that you'll fix with program assignment 1.
  2. jcsd
  3. Dec 18, 2011 #2


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    I never saw this question before, but I've seen WAY too much fortran code written in the same style as the solutions :devil:
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