/in/foo.c:1:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:1:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c:5:1: error: unknown type name 'bool'
 bool cmp(ll a , ll b) {return a > b;}
 ^~~~
/in/foo.c: In function 'main':
/in/foo.c:30:5: error: 'cin' undeclared (first use in this function)
     cin >> a >> b ; a -- ;
     ^~~
/in/foo.c:30:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:36:5: warning: implicit declaration of function 'sort' [-Wimplicit-function-declaration]
     sort(w + 1 , w + n + 1 , cmp);
     ^~~~
/in/foo.c:39:5: error: 'cout' undeclared (first use in this function)
     cout << b - a - ans;
     ^~~~