Compilare: user.cpp: In function ‘int main()’: user.cpp:40:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=1;j<=strlen(a[i]+1);j++) ^ user.cpp:7:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("trie.in","r",stdin); ^ user.cpp:8:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("trie.out","w",stdout); ^ user.cpp:12:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d ",&op); ^ user.cpp:14:18: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s+1); ^ user.cpp:15:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("\n"); ^ /tmp/ccLt8nmj.o: In function `main': user.cpp:(.text.startup+0xaa): warning: the `gets' function is dangerous and should not be used.