foo.cc: In function 'int main()':
foo.cc:50:5: error: redefinition of 'int main()'
 int main()
     ^~~~
foo.cc:23:5: note: 'int main()' previously defined here
 int main()
     ^~~~
foo.cc: In function 'int main()':
foo.cc:27:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~
foo.cc:29:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &a[i]);
         ~~~~~^~~~~~~~~~~~~

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