foo.c:3:1: error: unknown type name 'using'
    3 | using namespace std;
      | ^~~~~
foo.c:3:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    3 | using namespace std;
      |                 ^~~
foo.c: In function 'main':
foo.c:8:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    8 |  scanf("%s",a);
      |  ^~~~~~~~~~~~~
foo.c:9:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    9 |  scanf("%s",b);
      |  ^~~~~~~~~~~~~

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