/in/foo.c:2:1: error: unknown type name 'boll'
 boll 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:6:11: error: expected '=', ',', ';', 'asm' or '__attribute__' before '==' token
  for(int i==2; i<x; i++)
           ^~
/in/foo.c:6:16: error: 'i' undeclared (first use in this function)
  for(int i==2; i<x; i++)
                ^
/in/foo.c:6:19: error: expected ')' before ';' token
  for(int i==2; i<x; i++)
                   ^
/in/foo.c:6:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i==2; i<x; i++)
  ^~~
/in/foo.c:9:3: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
   return true;
   ^~~~~~
/in/foo.c:9:10: error: 'true' undeclared (first use in this function)
   return true;
          ^~~~
/in/foo.c: In function 'main':
/in/foo.c:18:19: error: 'true' undeclared (first use in this function)
   if(isPrime(x1)==true&&isPrime(x2)==true)
                   ^~~~
/in/foo.c: In function 'isPrime':
/in/foo.c:10:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^