/in/foo.cc: In function 'int main()':
/in/foo.cc:6:6: error: invalid operands of types 'double' and 'double' to binary 'operator^'
   a^=b;
      ^
/in/foo.cc:6:6: error:   in evaluation of 'operator^=(double, double)'
/in/foo.cc:7:6: error: invalid operands of types 'double' and 'double' to binary 'operator^'
   b^=a;
      ^
/in/foo.cc:7:6: error:   in evaluation of 'operator^=(double, double)'
/in/foo.cc:8:6: error: invalid operands of types 'double' and 'double' to binary 'operator^'
   a^=b;
      ^
/in/foo.cc:8:6: error:   in evaluation of 'operator^=(double, double)'