foo.cc:4:8: error: array bound is not an integer constant before ']' token
    4 | int a[i];
      |        ^
foo.cc: In function 'int main()':
foo.cc:11:8: error: 'a' was not declared in this scope
   11 |   cin>>a[i]
      |        ^
foo.cc:7:10: warning: unused variable 'i' [-Wunused-variable]
    7 |  int b,c,i;
      |          ^

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