foo.c:1:1: error: unknown type name 'using'
    1 | using namespace std;
      | ^~~~~
foo.c:1:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    1 | using namespace std;
      |                 ^~~
foo.c:2:9: fatal error: iostream: No such file or directory
    2 | #include<iostream>
      |         ^~~~~~~~~~
compilation terminated.

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