Compilare: user.cpp: In function ‘bool letter(char)’: user.cpp:4:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] return 'a'<=c&&c<='z'||'A'<=c&&c<='Z'; ^ user.cpp: In function ‘int main()’: user.cpp:10:18: warning: format ‘%d’ expects argument of type ‘int*’, but argument 2 has type ‘char*’ [-Wformat=] scanf("%d",&c); ^ user.cpp:8:33: 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:9:35: 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:10:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&c); ^