/in/foo.cc: In function 'int main()':
/in/foo.cc:7:2: error: expected ';' before 'r'
  r=1/(1/r1+1/r2)
  ^
/in/foo.cc:5:14: warning: unused variable 'r' [-Wunused-variable]
  float r1,r2,r;
              ^