foo.cc: In function 'int main()':
foo.cc:9:14: error: expected unqualified-id before '<<' token
    9 |         std::<<"十进制："<<dec<<"，二进制："<<conv_dec_to_bin(dec)<<std::endl
      |              ^~
foo.cc:9:47: error: 'conv_dec_to_bin' was not declared in this scope
    9 |         std::<<"十进制："<<dec<<"，二进制："<<conv_dec_to_bin(dec)<<std::endl
      |                                               ^~~~~~~~~~~~~~~
foo.cc:4:9: warning: unused variable 'bin' [-Wunused-variable]
    4 |     int bin=0;
      |         ^~~

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