/in/foo.c: In function 'main':
/in/foo.c:72:2: error: 'cin' undeclared (first use in this function)
  cin >> n;
  ^~~
/in/foo.c:72:2: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:71:8: warning: unused variable 'm' [-Wunused-variable]
  int n,m;
        ^