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:5:7: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>=' token
    5 |  int m>=5,n<500;
      |       ^~
foo.c:5:7: error: expected expression before '>=' token
foo.c:6:8: error: 'm' undeclared (first use in this function)
    6 |  int a[m=1]][n]
      |        ^
foo.c:6:8: note: each undeclared identifier is reported only once for each function it appears in
foo.c:6:12: error: expected '=', ',', ';', 'asm' or '__attribute__' before ']' token
    6 |  int a[m=1]][n]
      |            ^
foo.c:6:12: error: expected statement before ']' token
foo.c:6:13: error: expected expression before '[' token
    6 |  int a[m=1]][n]
      |             ^
foo.c:6:14: error: 'n' undeclared (first use in this function)
    6 |  int a[m=1]][n]
      |              ^
foo.c: At top level:
foo.c:9:8: error: expected '=', ',', ';', 'asm' or '__attribute__' before numeric constant
    9 | retrun 0;
      |        ^

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