/in/foo.c:2:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'main':
/in/foo.c:6:16: warning: format '%s' expects argument of type 'char *', but argument 2 has type 'char (*)[200]' [-Wformat=]
  while(scanf("%s",&u)==1)
                ^