foo.c:2:10: error: macro names must be identifiers
    2 | #define  5<n<1000
      |          ^
foo.c: In function 'main':
foo.c:6:15: error: 'n' undeclared (first use in this function)
    6 |         int a[n],i,j,t;
      |               ^
foo.c:6:15: note: each undeclared identifier is reported only once for each function it appears in
foo.c:6:13: warning: unused variable 'a' [-Wunused-variable]
    6 |         int a[n],i,j,t;
      |             ^

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