foo.cc: In function 'int main()':
foo.cc:7:30: error: invalid operands of types 'double' and 'double' to binary 'operator%'
  r=double(r1*r2/(r1+r2)+r1*r2%(r1+r2));
                         ~~~~~^~~~~~~~
foo.cc:6:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%lf %lf",&r1,&r2);
  ~~~~~^~~~~~~~~~~~~~~~~~~

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