Compilare: user.cpp: In function ‘int main()’: user.cpp:38:67: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] predecesor[1] = '-',predecesor[2]='1' , predecesor[3] = NULL; ^ user.cpp:53:61: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] succesor[1] = '-',succesor[2]='1' , succesor[3] = NULL; ^ user.cpp:8:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("calc.in","r",stdin); ^ user.cpp:9:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("calc.out","w",stdout); ^ user.cpp:11:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &instr); ^ user.cpp:12:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &n); ^ user.cpp:28:14: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s+1); ^ /tmp/cc8PvGqW.o: In function `main': user.cpp:(.text.startup+0x89): warning: the `gets' function is dangerous and should not be used.