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]
     scanf("%d",&n);  
     ~~~~~^~~~~~~~~
foo.cc:8:44: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for (int i=1;i<=n;i++)scanf("%d",&w[i]),sum+=w[i];  
                           ~~~~~~~~~~~~~~~~~^~~~~~~~~~

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