/in/foo.cc: In function 'int main()':
/in/foo.cc:5:9: warning: unused variable 's2' [-Wunused-variable]
    5 |  int s1,s2,r;
      |         ^~
/in/foo.cc:7:9: warning: 'r' is used uninitialized [-Wuninitialized]
    7 |  cout<<2*r-s1;
      |        ~^~
/in/foo.cc:5:12: note: 'r' was declared here
    5 |  int s1,s2,r;
      |            ^