递归实现：一个数的各位数字之和、n^k、字符串逆序

用递归求一个数的个位数字之和
#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<windows.h>
int qiuhe(int a)
{
if (a == 0)
return 0;
else
return(a % 10 + qiuhe(a / 10));
system("pause");
}
void main()
{
printf("%d\n",qiuhe(2345));
getchar();
/*system("pause");*/
}

用递归实现N的K次方
#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<windows.h>
int fun(int n, int k)
{
int sum;
if (k == 0)
{
sum = 1;
}
else
{
sum = n*fun(n, k - 1);
}
return sum;
}
int main()
{
printf("%d\n", fun(2, 3));
system("pause");
return 0;
}

用递归实现字符串的字符反转
#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<windows.h>
void rev_print(char *x )
{
if (*x)
rev_print(x + 1);
else
return;
putchar(*x);

}
int main(void)
{
char line[80];
printf("请输入一个字符串:");
gets(line);
rev_print(line);
system("pause");
return 0;
}