foo.c:2:1: error: unknown type name 'using'
    2 | using namespace std;
      | ^~~~~
foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    2 | using namespace std;
      |                 ^~~
foo.c: In function 'main':
foo.c:5:9: error: array size missing in 'x'
    5 |     int x[];
      |         ^
foo.c:6:9: warning: unused variable 'm' [-Wunused-variable]
    6 |  int  n,m;
      |         ^
foo.c:6:7: warning: unused variable 'n' [-Wunused-variable]
    6 |  int  n,m;
      |       ^
foo.c:5:9: warning: unused variable 'x' [-Wunused-variable]
    5 |     int x[];
      |         ^
foo.c: At top level:
foo.c:9:1: error: expected identifier or '(' before 'return'
    9 | return 0;
      | ^~~~~~

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