/in/foo.cc: In function 'int main()':
/in/foo.cc:10:6: warning: unused variable 'cnt' [-Wunused-variable]
  int cnt = 0;
      ^~~
/in/foo.cc:7:20: warning: 'n' is used uninitialized in this function [-Wuninitialized]
  for (int i = 0; i < n; i++)
                  ~~^~~
/in/foo.cc:13:4: warning: 'm' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (a[i] + a[j] == m) {
    ^~