foo.c: In function 'main':
foo.c:7:21: error: 'n' undeclared (first use in this function)
    7 |         scanf("%d",&n);
      |                     ^
foo.c:7:21: note: each undeclared identifier is reported only once for each function it appears in
foo.c:8:13: error: 'i' undeclared (first use in this function)
    8 |         for(i=0;i<=n;i++)
      |             ^
foo.c:15:13: error: 'j' undeclared (first use in this function)
   15 |         for(j=0;j<=n;j++)
      |             ^
foo.c:6:13: warning: variable 'a' set but not used [-Wunused-but-set-variable]
    6 |         int a[1000];
      |             ^

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