foo.cc: In function 'void insert(char*)':
foo.cc:27:34: warning: array subscript has type 'char' [-Wchar-subscripts]
   27 |                         s[k+1]=s[k];
      |                                  ^
foo.cc:28:19: warning: array subscript has type 'char' [-Wchar-subscripts]
   28 |                 s[j]=',';
      |                   ^
foo.cc: In function 'int main()':
foo.cc:40:22: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
   40 |         for(int i=0;i<strlen(s);i++)
      |                     ~^~~~~~~~~~

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