Compilare: user.cpp: In function ‘bool letter(char)’: user.cpp:6:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] return 'a'<=c&&c<='z'||'A'<=c&&c<='Z'; ^ user.cpp: In function ‘int main()’: user.cpp:9:33: 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:10:35: 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); ^ user.cpp:11:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); ^ /tmp/ccnEmK7u.o: In function `main': user.cpp:(.text.startup+0x56): warning: the `gets' function is dangerous and should not be used.