foo.cc: In function ‘int solve(int, int, int)’:
foo.cc:23:9: error: ‘_itoa’ was not declared in this scope
   23 |         _itoa(yu,str,p);
      |         ^~~~~
foo.cc:24:23: warning: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Wsign-compare]
   24 |         for (int i=0;i<strlen(str);i++)
      |                      ~^~~~~~~~~~~~