Compilare: user.cpp: In function ‘int main()’: user.cpp:20:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cifra.in","r",stdin); ^ user.cpp:21:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cifra.out","w",stdout); ^ user.cpp:22:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &n); ^ user.cpp:25:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); x=strlen(s); ^ user.cpp: In function ‘void det()’: user.cpp:17:15: warning: array subscript is above array bounds [-Warray-bounds] a[0]=a[100]; ^ user.cpp:15:15: warning: iteration 21u invokes undefined behavior [-Waggressive-loop-optimizations] a[i]=s; ^ user.cpp:9:5: note: containing loop for (i=1;i<=100;i++) { ^ user.cpp:14:13: warning: ‘ucf’ may be used uninitialized in this function [-Wmaybe-uninitialized] s=(s+ucf)%10; ^ /tmp/ccalYE92.o: In function `main': user.cpp:(.text.startup+0xda): warning: the `gets' function is dangerous and should not be used.