foo.c:1:2: error: unknown type name 'using'
    1 |  using namespace std;
      |  ^~~~~
foo.c:1:18: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    1 |  using namespace std;
      |                  ^~~
foo.c:2:11: fatal error: iostream: No such file or directory
    2 | # include <iostream>
      |           ^~~~~~~~~~
compilation terminated.

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