/in/foo.c:2:1: error: unknown type name 'bool'
 bool isPrime(int n)
 ^~~~
/in/foo.c: In function 'isPrime':
/in/foo.c:6:16: error: 'false' undeclared (first use in this function)
         return false;
                ^~~~~
/in/foo.c:6:16: note: each undeclared identifier is reported only once for each function it appears in