foo.cc:3:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
    3 | main()
      |      ^
foo.cc: In function 'int main()':
foo.cc:7:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    7 |     scanf("%d",&n);
      |     ~~~~~^~~~~~~~~

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