/in/foo.cc: In function 'int main()':
/in/foo.cc:7:12: warning: right operand of comma operator has no effect [-Wunused-value]
  cin>>s,r1,r2; 
            ^~
/in/foo.cc:7:14: warning: right operand of comma operator has no effect [-Wunused-value]
  cin>>s,r1,r2; 
              ^
/in/foo.cc:8:4: warning: 'r1' is used uninitialized in this function [-Wuninitialized]
  r2=s*2-r1;
  ~~^~~~~~~