Author:

• Name: Ian Collier
  Location: GB - United Kingdom of Great Britain and Northern Ireland (United Kingdom)

To build:

    make all

To use:

    ./imc number

where number is an optional number. Default is 5.

Try:

    ./try.sh

Judges’ remarks:

This entry’s algorithm is as magic as its output!

Author’s remarks:

This program may be compiled with an ANSI or K&R compiler. A few harmless warnings are displayed only if gcc -Wall is used.

This entry is really a set of library functions, but an example main() function has been added so that the library can be tested. If the program appears too large, consider that functions o() and s() can each be separated from the rest of the program (except for the short functions p() and r(), which they require) and used alone. However, the main part of the program is the function e, which does require all the other functions (apart from main()).

The program should be supplied with an integer parameter. If no parameter or an invalid parameter is given, then 5 is assumed. The maximum parameter is determined only by the amount of CPU time, virtual memory and display (or file) space available.

NOTICE to those who wish for a greater challenge:

If you want a greater challenge, don’t read any further: just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.

How this entry works:

OK, so you have probably seen magic square printers before. But what about one that deals with even sizes as well as odd ones, or one that prints out a different one each time (or attempts to, at any rate)?

I have formatted the important functions o(), s() and e() to show how useful the word for is, and (in function e()) how useful the words if and else are. In fact, hardly anything happens that isn’t in one of these instructions. I did this in order to simplify the code - the algorithms used to make the random squares are quite complex without being shrouded in obfuscated code! :-) Incidentally, I was surprised to find out how useful the exclusive-or operator was while writing function s().

Here are the descriptions of the functions in the library:

o(n,a,q,d): makes a magic square of order n when n is odd and at least 3.
s(n,a,q,d): makes a magic square of order n when n equals 4.
e(n,a,q,d): makes a magic square of order n when n is even and at least 6.

In the above, a (of type int *) points to an area of memory in which the magic square will be stored and q (also of type int *) points to an area of memory of length at least n*sizeof(int) bytes which can be used as a work space. Both a and q must be allocated by the caller. The integer parameter d, usually zero, indicates the length of a gap which will be left between adjacent rows of the magic square.

The square which is returned will (or should) be a permutation of the numbers 1 to n*n in which all rows and columns and the two diagonals add up to n*(n*n+1)/2.

Primary files

• imc.c - entry source code
• Makefile - entry Makefile
• imc.orig.c - original source code
• try.sh - script to try entry

Secondary files

• 1994_imc.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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