/in/foo.cc: In function 'int main()':
/in/foo.cc:23:17: warning: format '%f' expects a matching 'double' argument [-Wformat=]
  printf("%.2f,r");
                 ^
/in/foo.cc:5:17: warning: variable 'r' set but not used [-Wunused-but-set-variable]
     float n1,n2,r;
                 ^