Compilare: user.cpp: In function ‘void read()’: user.cpp:14:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("expr.in", "r", stdin); ^ user.cpp:15:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s + 1); ^ user.cpp: In function ‘void write()’: user.cpp:131:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("expr.out", "w", stdout); ^ /tmp/ccBHu1qv.o: In function `read()': user.cpp:(.text+0x30): warning: the `gets' function is dangerous and should not be used.