Compilare: user.cpp: In function ‘void backtr(int)’: user.cpp:12:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if( niv == s.length() + 1 ) ^ user.cpp:15:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0 ; i < s.length() ; i++ ) ^ user.cpp:23:17: warning: array subscript has type ‘char’ [-Wchar-subscripts] frc[ it ]++; ^ user.cpp:28:25: warning: array subscript has type ‘char’ [-Wchar-subscripts] if( frc[ it ] ) ^ user.cpp:29:44: warning: array subscript has type ‘char’ [-Wchar-subscripts] mini = min( mini , frc[ it ] ); ^ user.cpp:30:40: warning: array subscript has type ‘char’ [-Wchar-subscripts] maxi = max( maxi , frc[ it ] ); ^ user.cpp:34:17: warning: array subscript has type ‘char’ [-Wchar-subscripts] frc[ it ]--; ^ user.cpp: In function ‘int main()’: user.cpp:40:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( i = 0 ; i < s.length() ; i++ ) ^ user.cpp:42:25: warning: array subscript has type ‘char’ [-Wchar-subscripts] if( frc[ s[ i ] ] == 0 ) ^ user.cpp:44:25: warning: array subscript has type ‘char’ [-Wchar-subscripts] frc[ s[ i ] ] = 1; ^