Question

I have two unrelated questions:

1. Is it possible to use #define to define something other than a number? (Such as an extended ASCII character).

2. Is it considered good practice to use preprocessor directives within the main() function? The only reason I would ever think to do this is to execute different code depending on which OS is being run.

Answer 1

Object-like macros (#define macros with no arguments) are simply replacements. So anything that might otherwise be in your code can be the replacement, for example a literal string: #define PROGRAM_NAME "MyProgram", or multi-line code blocks. Here’s a useless example of the latter:

#define INFINITE_PRINTF while (1) \
                        { \
                            printf("looping..."); \
                        }

As for the second question, it is common practice to use preprocessor directives throughout C code to do just what you’ve mentioned: conditionally including/excluding code, in main and elsewhere. Occasionally I’ll use #define for constants near where they’ll be used, for clarity.