foo.cc:6:8: warning: converting to non-pointer type 'int' from NULL [-Wconversion-null]
    6 |  int n=NULL;
      |        ^~~~
foo.cc: In function 'int main()':
foo.cc:68:8: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result]
   68 |  system("pause");
      |  ~~~~~~^~~~~~~~~

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