Why does the code fail?

Question

C++ / C#

#include <stdio.h>
#include <stdlib.h>
#include <locale.h>
#include <ctype.h>

int main()
{
    setlocale(LC_ALL,"Rus");
    char  a;
    scanf("%s",a);
    printf("%s",a);
    int num;
    num = atoi(a);
    printf("%d",num);
    return 0;
}

Answer 1

the scanf function works with pointers, so you had to pass not "a" as a parameter, but an address pointing to "a", in other words, write: scanf("%s", &a)

Answer 2

because the pointer "a" is not clear where it points, and you are not sure where else you are trying to organize input from the keyboard, and as a result you get it is not clear what.