I had to compile a 32-bit application using GNU gcc on the 64-bit version Linux.
Luckily gcc man page directed me to -m32 and -m64 option. These options generate code for a 32-bit or 64-bit environments.
=> The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any i386 system.
=> The 64-bit environment sets int to 32 bits and long and pointer to 64 bits and generates code for AMD's x86-64 architecture.
You can pass -m64 or -m32 as follows
For 32 bit version:
$ gcc -m32 -o output32 hello.c
For 64 bit version :
$ gcc -m64 -o output64 hello.c