样例二：计算圆周率

 1 #include<iostream>
 2 #include<cmath>
 3 using namespace std;
 4 
 5 #define r 1
 6 
 7 /*
 8 计算2^n边型的单边边长
 9 */
10 double singleLength(int n) {
11     if (n == 2)
12         return sqrt(2)*r;
13     double sinalphad2 = singleLength(n - 1) / (2 * r);
14     double cosalphad2 = sqrt(1 - sinalphad2*sinalphad2);
15     double sinalphad4 = sqrt((1 - cosalphad2) / 2);
16     double y = 2 * r*sinalphad4;
17     return y;
18 }
19 
20 int main() {
21     int n;
22     cout << "最多计算到2^n边型，n=";
23     cin >> n;
24     
25     double length = singleLength(n)*pow(2.0,(double)n);
26     cout.precision(20);
27     cout << "估算的周长为：" << fixed << length << endl;
28     cout << "估算的圆周率为：" << fixed << length / (2 * r) << endl;
29     return 0;
30 }