Compilare: user.cpp: In function ‘int main()’: user.cpp:23:17: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] if(s[i]>='A'&&s[i]<='Z'||s[i]>='a'&&s[i]<='z'||s[i]>='0'&&s[i]<='9') ^ user.cpp:23:61: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] if(s[i]>='A'&&s[i]<='Z'||s[i]>='a'&&s[i]<='z'||s[i]>='0'&&s[i]<='9') ^ user.cpp:31:19: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s1[cate++]=NULL; ^ user.cpp:49:19: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s1[cate++]=NULL; ^ user.cpp:77:18: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] a1[j].s[c3++]=NULL; ^ user.cpp:17:28: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dir.in","r",stdin); ^ user.cpp:18:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dir.out","w",stdout); ^ user.cpp:19:8: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); ^ /tmp/ccU0BGgy.o: In function `main': user.cpp:(.text.startup+0x5b): warning: the `gets' function is dangerous and should not be used.