/in/foo.cc: In function 'int main()':
/in/foo.cc:13:23: warning: 'n' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<"gcd="<<gcd(m,n)<<endl;
                       ^
/in/foo.cc:5:6: warning: 'm' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if(m%n==0) return n;
     ~^~
/in/foo.cc:11:8: note: 'm' was declared here
  int t,m,n;
        ^