Compilare: main.cpp: In function 'void add_dfs(node*, std::string, int)': main.cpp:21:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 21 | if( i >= str.size() ) { | ~~^~~~~~~~~~~~~ main.cpp: In function 'int del_dfs(node*, std::string, int)': main.cpp:34:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 34 | if( i >= str.size() ) { | ~~^~~~~~~~~~~~~ main.cpp: In function 'int app_dfs(node*, std::string, int)': main.cpp:56:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 56 | if( i >= str.size() ) | ~~^~~~~~~~~~~~~ main.cpp: In function 'int pref_dfs(node*, std::string, int)': main.cpp:64:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 64 | if( i >= str.size() ) | ~~^~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:74:10: warning: unused variable 'ch' [-Wunused-variable] 74 | char ch; | ^~