Compilare: main.cpp: In function 'void add()': main.cpp:37:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 0 ; i < s.size() ; ++ i ) { ~~^~~~~~~~~~ main.cpp: In function 'int sub(node*, int)': main.cpp:49:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( i != s.size() ) { ~~^~~~~~~~~~~ main.cpp:55:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( i == s.size() ) { ~~^~~~~~~~~~~ main.cpp: In function 'int count()': main.cpp:72:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 0 ; i < s.size() ; ++ i ) { ~~^~~~~~~~~~ main.cpp: In function 'int length()': main.cpp:84:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 0 ; i < s.size() ; ++ i ) { ~~^~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:95:9: warning: unused variable 'x' [-Wunused-variable] int x , y , i ; ^ main.cpp:95:13: warning: unused variable 'y' [-Wunused-variable] int x , y , i ; ^ main.cpp:95:17: warning: unused variable 'i' [-Wunused-variable] int x , y , i ; ^