/in/foo.c:4:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:4:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c:12:9: error: unknown type name 'DATA'
 int cmp(DATA a, DATA b) 
         ^~~~
/in/foo.c:12:17: error: unknown type name 'DATA'
 int cmp(DATA a, DATA b) 
                 ^~~~
/in/foo.c: In function 'main':
/in/foo.c:32:42: error: 'cmp' undeclared (first use in this function)
  qsort(person + 1, n, sizeof(person[0]), cmp);  //用快速排序对W和num同时排序
                                          ^~~
/in/foo.c:32:42: note: each undeclared identifier is reported only once for each function it appears in