/in/foo.c:2:1: error: unknown type name 'bool'
 bool isPrime(int x)
 ^~~~
/in/foo.c: In function 'isPrime':
/in/foo.c:5:10: error: 'false' undeclared (first use in this function)
   return false;
          ^~~~~
/in/foo.c:5:10: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:3: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   if(x%i==0)
   ^~
/in/foo.c:9:4: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'if'
    return true;
    ^~~~~~
/in/foo.c:9:11: error: 'true' undeclared (first use in this function)
    return true;
           ^~~~
/in/foo.c: In function 'main':
/in/foo.c:18:18: error: 'true' undeclared (first use in this function)
   if(isPrime(x)==true &&isPrime(x2)==true)
                  ^~~~
/in/foo.c: In function 'isPrime':
/in/foo.c:10:2: warning: control reaches end of non-void function [-Wreturn-type]
  }
  ^