foo.cc: In function 'int main()':
foo.cc:20:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < s.length(); i++)
                     ~~^~~~~~~~~~~~
foo.cc:42:11: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result]
     system("pause");
     ~~~~~~^~~~~~~~~

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