foo.c: In function 'main':
foo.c:29:6: error: 'i' undeclared (first use in this function)
   29 |  for(i=1;i<=n;i++)
      |      ^
foo.c:29:6: note: each undeclared identifier is reported only once for each function it appears in
foo.c:31:7: error: 'j' undeclared (first use in this function)
   31 |   for(j=1;j<=n;j++)
      |       ^

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