#include <stdio.h>

char *small (char *num)
{
    static int i=0;
    if (num[i+1] == '\0')
        return NULL;
    if (num[i] > num[i+1])
		return &num[i];
    printf("%c, %c", num[i],num[i+1]);
    i++;
    return small(num);
}

int main()
{
    char *c = "1234";
    char *p = small(c);
    if (p == NULL)
        printf("null");
    else
        printf("%c",*p);
    return 0;
}