foo.cc:2:11: error: '::main' must return 'int'
 void main()
           ^
foo.cc: In function 'int main()':
foo.cc:5:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d",&n);
 ~~~~~^~~~~~~~~

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