Question

For example, I’m supposed to convert “int” to “INT”. But if there’s the word “integer”, I don’t think it’s supposed to turn into “INTeger”.

If I define "int" printf("INT"); the substrings are matched though. Is there a way to prevent this from happening?

Answer 1

I believe the following captures what you want.

%{
#include <stdio.h>
%}

ws                      [\t\n ]

%%

{ws}int{ws}         { printf ("%cINT%c", *yytext, yytext[4]); }
.                       { printf ("%c", *yytext); }

To expand this beyond word boundaries ({ws}, in this case) you will need to either add modifiers to ws or add more specifc checks.