foo.cc: In function 'int main()':
foo.cc:58:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   58 |  scanf("%d",&n);
      |  ~~~~~^~~~~~~~~
foo.cc:60:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   60 |   scanf("%1d",&a);//坑3，小技巧%1d只读一位
      |   ~~~~~^~~~~~~~~~

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