/in/foo.cc: In function 'int main()':
/in/foo.cc:23:4: error: 's' was not declared in this scope
    s+=t;
    ^
/in/foo.cc:26:24: error: 's' was not declared in this scope
  cout << cnt << " " << s;
                        ^
/in/foo.cc:5:22: warning: unused variable 'a' [-Wunused-variable]
  int A,B,n,m,t,cnt=0,a=0;
                      ^