Compilare: user.cpp: In function ‘void sum(int, int)’: user.cpp:38:7: warning: operation on ‘l’ may be undefined [-Wsequence-point] c[++l] = l; ^~~ user.cpp: In function ‘int main()’: user.cpp:47:5: warning: ‘char* gets(char*)’ is deprecated [-Wdeprecated-declarations] gets(a + 1); ^~~~ In file included from /usr/include/c++/6/cstdio:42:0, from user.cpp:1: /usr/include/stdio.h:638:14: note: declared here extern char *gets (char *__s) __wur __attribute_deprecated__; ^~~~ user.cpp:47:15: warning: ‘char* gets(char*)’ is deprecated [-Wdeprecated-declarations] gets(a + 1); ^ In file included from /usr/include/c++/6/cstdio:42:0, from user.cpp:1: /usr/include/stdio.h:638:14: note: declared here extern char *gets (char *__s) __wur __attribute_deprecated__; ^~~~ user.cpp:43:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("next.in", "r", stdin); ^ user.cpp:44:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("next.out", "w", stdout); ^ user.cpp:47:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a + 1); ^ user.cpp:49:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%lld", &k); ^ user.cpp: In function ‘void sum(int, int)’: user.cpp:37:3: warning: ‘r’ may be used uninitialized in this function [-Wmaybe-uninitialized] if(r != 0) ^~ /tmp/ccZG2tXD.o: In function `main': user.cpp:(.text.startup+0x54): warning: the `gets' function is dangerous and should not be used.