gcc programming
 

Just trying out gcc I copied a temp' conversion program and compiled it with no errors

temp.c -o temp

and sent it to a friend to try out on their windows machine, they said it caused a "this program has performed illegal operation", so sent it to another friend and they said it ran but was unable to enter anything.

Is there something that needs to be done in program for it to run on windows machine or something ?

linux executables will not run on windows.... you would need a unix later such as cygwin to run them....

So there is no way I could write a small C program on Linux, that would run on a windows machine ?

A program written in C will work fine.... if compiled independently on diferent operating systems... so if u want ur c program to work on different operating systems then u have to compile ur c source code indepently on the different os....
In ur case u just have to compile with a c compiler like gcc which is available on both the oses (linux & windows).... it will work fine....