Compilare: user.cpp: In function ‘bool litera(char)’: user.cpp:9:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] return 'a'<=c&&c<='z'||'A'<=c&&c<='Z'; ^ user.cpp: In function ‘int main()’: user.cpp:25:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();) ^