c语言 深入理解函数的递归

#include<stdio.h>//打印一个整数的每一位,用递归
print(int n)
{
	int i = 0;
	if(n>9)
	{
		print(n / 10);
	}
	printf("%d", n%10);
}
int main()
{
	int num = 0;
	printf("请输入一个整数：");
	scanf("%d",&num);
	print(num);
	return 0;
}

#include<stdio.h>//求n的阶乘
int main()
{
	int num = 0; int i = 0; int ret = 1;
	printf("请输入一个值：");
	scanf("%d",&num);
	for (i = 2; i <=num; i++)
	{
		ret *= i;
	}
	printf("%d", ret);
	return 0;
}

#include<stdio.h>//求n的阶乘
int fac(int n)
{
	if (n > 1)
		return n * fac(n - 1);
	else
		return 1;
}
int main()
{
	int ret = 0;
	int num = 0;
	printf("请输入n的值：");
	scanf("%d", &num);
	ret=fac(num);
	printf("%d", ret);
	return 0;
}

#include<stdio.h>//用非递归求字符串的长度
my_strlen(char *arr)
{
	int a = 0; int ret = 0;
	char c = *(arr+a);
	while(arr[a] != '\0')
	{
		a++;
		ret++;
		}
	return ret;
}
int main()
{
	int ret = 0;
	char arr[] = "abc";
	ret=my_strlen(arr);
 	printf("%d", ret);
	return 0;
}

#include<stdio.h>
my_strlen(char* arr)
{
	int i = 0;
	if (*arr == '\0')
		return 0;
	if (*arr != '\0')
		return 1 + my_strlen(arr + 1);
}
int main()
{
	int ret = 0;
	char arr[] = "abc";
	ret = my_strlen(arr);
	printf("%d", ret);
	return 0;
}

#include<stdio.h>//输入一个数求各位数之和
sum(int x)
{
	int ret = 0;
	if (x > 9)
	{
		return  x % 10 + sum(x / 10);
	}
	else
		return x;
}
int main()
{
	int num = 0;
	printf("请输入一个数之和：");
	scanf("%d", &num);
	printf("%d",sum(num));
	return 0;
}

#include<stdio.h>//用递归求n的k次方
tmp(int x,int y)
{
	if (y <= 0)
	{
		return 1;
	}
	else
		return x * tmp(x, y - 1);
}
int main()
{
	int k = 0; int n = 0;
	printf("请输入一个n和k：");
	scanf("%d %d",&n, &k);
	int ret=tmp(n,k);
	printf("%d", ret);
	return 0;
}

#include<stdio.h>//计算斐波那契数
feibona(int n)
{
	
	if (n >= 3)
		return feibona(n - 1) + feibona(n - 2);
	else 1;
}
int main()
{
	int n = 0;
	printf("请输入一个n：");
	scanf("%d", &n);
	int ret=feibona(n);
	printf("%d", ret);
	return 0;
}

#include<stdio.h>//用非递归求斐波那契数\
int feibona(int N)
{
int i = 1;
int j = 1;
int sum = i + j;
for (i = 4; i <= N; i++)
{
	i = j;
	j = sum;
	sum = i + j;
}
return sum;
}
int main()
{
	printf("请输入一个n：");
	scanf("%d",&n);
	int ret=feibona(n);
	printf("%d", ret);
	return 0;
}