Compilare: user.cpp: In function ‘int main()’: user.cpp:18:12: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] st[++k]=NULL; ^ user.cpp:5:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("trompeta.in","r",stdin); ^ user.cpp:6:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("trompeta.out","w",stdout); ^ user.cpp:8:28: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d %d\n",&n,&m); ^ user.cpp:9:13: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets (s); ^ /tmp/ccF4c0YG.o: In function `main': user.cpp:(.text.startup+0x72): warning: the `gets' function is dangerous and should not be used.