Ubuntu Linux cross-compiling 32bit binaries on a on 64bit system

First you need to to install the 32bit development environment
sudo apt-get install libc6-dev-i386

for g++ you will need the multi version of the library package 
sudo apt-get install g++-multilib

Second. when you compile you application specify the -m32 flag, either via the command line, or with the CFLAGS environment variable
gcc -m32 -o program program.c

Cross compiling with mingw32msvc

when using "autoconfig" configure set the following flags

./configure \
--prefix=/usr/i586-mingw32msvc \

Useful C Compiler directives

__LINE__    The current line number
__FILE__    The current file name
printf("I am over here: line %d, in file %s\n", __LINE__, __FILE__);


to create a patch use
diff -rupN <> <>
to apply a patch use
patch -p1 < patch file