Compilare: user.cpp: In function ‘void make_sfx()’: user.cpp:33:29: warning: suggest parentheses around ‘-’ inside ‘<<’ [-Wparentheses] if(i + (1 << lg - 1) < len) ^ user.cpp:34:50: warning: suggest parentheses around ‘-’ inside ‘<<’ [-Wparentheses] l[i].c2 = p[lg - 1][i + (1 << lg - 1)]; ^ user.cpp: In function ‘int main()’: user.cpp:60:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("substr.in", "r", stdin); ^ user.cpp:61:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("substr.out", "w", stdout); ^ user.cpp:66:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d ",&len,&k); ^ user.cpp:67:14: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(str); ^ /tmp/ccb7GjEm.o: In function `main': user.cpp:(.text.startup+0x72): warning: the `gets' function is dangerous and should not be used.