foo.cc: In constructor 'Charz::Charz()':
foo.cc:24:13: warning: unused variable 'i' [-Wunused-variable]
   24 |         int i;
      |             ^
foo.cc: In member function 'int Charz::Length(char*)':
foo.cc:42:28: warning: value computed is not used [-Wunused-value]
   42 |         for (; *a != '\0'; *a++, i++) {}
      |                            ^~~~
foo.cc: In member function 'Charz& Charz::Concat(Charz&)':
foo.cc:80:16: warning: reference to local variable 'c' returned [-Wreturn-local-addr]
   80 |         return c;
      |                ^
foo.cc:74:15: note: declared here
   74 |         Charz c(*this);
      |               ^

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