Compilare: user.cpp: In function ‘bool is_letter(char)’: user.cpp:18:42: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] bool is_letter(char c) { return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z'; } ^ user.cpp: In function ‘int main()’: user.cpp:37:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("text.in", "r", stdin); ^ user.cpp:38:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("text.out", "w", stdout); ^