foo.cc: In function 'long long int once(long int, long int)':
foo.cc:11:36: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   for (int i = number_after + 1; i = 1; i--)
                                  ~~^~~
foo.cc:15:38: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   for (size_t i = number_before+1; i =1; i--)
                                    ~~^~
foo.cc:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (size_t i =1; i <= number_after-number_before; i++)
                     ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:25:40: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   for (size_t i = number_before + 1; i = 1; i--)
                                      ~~^~~
foo.cc:29:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (size_t i = 1; i <= number_before - number_after; i++)
                      ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:46:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (size_t i = 0; i < len_s; i++)
                     ~~^~~~~~~
foo.cc:48:12: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   if (s[i] = '5') {
       ~~~~~^~~~~

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