foo.cc: In function ‘int main()’:
foo.cc:4:1: error: ‘gets’ was not declared in this scope
    4 | gets(num);
      | ^~~~
foo.cc:7:11: error: ‘strlen’ was not declared in this scope
    7 | int len = strlen(ch);
      |           ^~~~~~
foo.cc:1:1: note: ‘strlen’ is defined in header ‘<cstring>’; this is probably fixable by adding ‘#include <cstring>’
  +++ |+#include <cstring>
    1 | int main()
foo.cc:16:1: error: ‘printf’ was not declared in this scope
   16 | printf("%s", ch);
      | ^~~~~~
foo.cc:1:1: note: ‘printf’ is defined in header ‘<cstdio>’; this is probably fixable by adding ‘#include <cstdio>’
  +++ |+#include <cstdio>
    1 | int main()