/in/foo.c:3:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:3:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'main':
/in/foo.c:7:5: error: 'cin' undeclared (first use in this function)
     cin>>xmin>>xmax;
     ^~~
/in/foo.c:7:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:8:9: error: expected identifier or '(' before numeric constant
     int 1;
         ^
/in/foo.c:11:9: error: 'i' undeclared (first use in this function)
         i+=ii;
         ^
/in/foo.c:12:5: error: 'cout' undeclared (first use in this function)
     cout<<i;
     ^~~~