C++递归

递归：函数（除main()以外）可以调用自己。

1.包含一个递归调用的递归： 如果递归函数调用自己，则被调用函数也将调用自己，这将无限循环下去，除非代码中包含终止调用链的内容。通常的方法将递归调用放在if语句中。例如：

 void recurs(argumentlist)
 {
 statements1
 if(test)
       recurs(arguments)
 statements2
 }

test最终为false，调用链将断开。

 #include<iostream>
 using namespace std;
 
 void countdown(int n);
 
 int main()
 {
 	countdown(4);
 	return 0;
 }
 
 void countdown(int n)
 {
 	cout << "Counting down ... " << n << endl;
 	if (n < 0)
	countdown(n);
 	cout << n << ": Kaboom\n";
 }

2.包含多个递归调用的递归

  #include<iostream>
const int Len = 66;
const int Divs = 6;
void subdivide(char ar[], int low, int high, int level);
int main()
{
	char ruler[Len];
	int i;
	for (i = 1; i < Len - 2; i++)
		ruler[i] = ' ';
	ruler[Len - 1] = '\0';
	int max = Len - 2;
	int min = 0;
	ruler[min] = ruler[max] = '|';
	std::cout << ruler << std::endl;
	for (i = 1; i <= Divs; i++)
	{
		subdivide(ruler, min, max, i);
		std::cout << ruler << std::endl;
		for (int j = 1; j <Len - 2; j++)
			ruler[j] = ' ';
	}
	return 0;
}

void subdivide(char ar[], int low, int high, int level)
{
	if (level == 0)
		return;
	int mid = (high + low) / 2;
	ar[mid] = '|';
	subdivide(ar, low, mid, level - 1);
	subdivide(ar, mid, high, level - 1);
}