/in/ex4.c: In function 'main':
/in/ex4.c:12:47: warning: passing argument 4 of 'strftime' from incompatible pointer type [-Wincompatible-pointer-types]
     strftime(buffer, 26, "%Y-%m-%d %H:%M:%S", a);
                                               ^
In file included from /in/ex4.c:2:0:
/usr/include/time.h:205:15: note: expected 'const struct tm * restrict' but argument is of type 'char *'
 extern size_t strftime (char *__restrict __s, size_t __maxsize,
               ^~~~~~~~
/in/ex4.c:10:16: warning: unused variable 'tm_info' [-Wunused-variable]
     struct tm* tm_info;
                ^~~~~~~
/in/ex4.c:8:12: warning: unused variable 'timer' [-Wunused-variable]
     time_t timer;
            ^~~~~
/in/ex4.c:7:5: warning: 'a' is used uninitialized in this function [-Wuninitialized]
     scanf("%c",a);
     ^~~~~~~~~~~~~