OK - so it's a bit of a problem in the translation into English, then!

Those are what we call "error messages" or similar.

The messages themselves are not wrong; in fact, they are perfectly correct! They are pointing-out things that are wrong with your source code


As Jan explained, 'C' does not allow executable statements outside functions. Therefore, the compiler takes anything outside a function to be a definition.
Since rd_wr was previously defined, this must be a re-definition - which is not allowed.


All identifiers - ie, variable names, function names, etc - must be defined (or declared) before they are used.
Because your definition of 'm' was invalid (see other error messages), it doesn't count. Hence 'm' effectively has no definition - in other words, it is undefined.

You will often find that one error leads to a string of others - so always fix the earliest error first!


Same as for 'm'


Jan also explained this one.


You would be far better advised to just pick one compiler and stick with it - chopping and changing between different compilers will only confuse you at this stage!