solution.cpp

#include <stdio.h>
int len(int x)
{
    if (x < 10)
        return 1;
    return len(x / 10) + 1;
}
// 取x的第k位数字
int f(int x, int k)
{
    if (len(x) - k == 0)
        return x % 10;
    return f(x / 10, k); //填空
}
int main()
{
    int x = 23574;
    printf("%d\n", f(x, 3));
    return 0;
}