/in/foo.c:3:21: error: expected ';', ',' or ')' before '&' token
 int judge(const int &x)
                     ^
/in/foo.c: In function 'main':
/in/foo.c:14:6: warning: implicit declaration of function 'judge' [-Wimplicit-function-declaration]
 if (!judge(s1[strlen(s1)-1]-48)) printf("MengMeng\n");
      ^~~~~