Compilare: main.cpp: In function 'bool is_digit(char)': main.cpp:19:21: warning: suggest parentheses around '&&' within '||' [-Wparentheses] return a >= 'A' && a <= 'Z' || a >= 'a' && a <= 'z'; ~~~~~~~~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:24:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i){ ~~^~~~~~~~~~ main.cpp:29:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i){ ~~^~~~~~~~~~