• FreeBSD
• clang / gcc

When attempting to compile a C program, in either clang or gcc, you encounter an error similar to this one:

myprogram.c:600:2: error: use of undeclared identifier 'uint'; did you mean 'int'?
        uint n=0;
        ^~~~
        int

uint is not a standard C data type, so it must be declared.

Include the sys/types.h header file before main in the C source file:

#include <sys/types.h> 

The program should then compile.