foo.cc: In function 'int main()':
foo.cc:15:16: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
   15 |  for (i = 1; i < strlen(s1); i++) {
      |              ~~^~~~~~~~~~~~
foo.cc:11:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   11 |  scanf("%s", s1);
      |  ~~~~~^~~~~~~~~~

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