Loops.c，RUN

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>
//Loops

//实现函数：
//sin(x)=x/1! - (x^3)/3! + (x^5)/5! - (x^7)/7! + …
//其中|x|<1，且最后一项精度不低于0.000001
//用for循环
double _sin(double x)
{
	double sum = 0.0;
	double precision = 0.000001;

	double item = x / 1.0;
	for (int i = 1; fabs(item) >= precision; i++)
	{
		sum = sum + item;
		item = -1.0 * item * x * x / (2 * i) / (2 * i + 1);
	}
	return sum;
}


//圆周率PI 
//PI / 4 = 1 - 1 / 3 + 1 / 5 - 1 / 7 + .....，
//最后一项绝对值不小于0.000001，不过结果收敛并不好
//用do while循环
double PI()
{
	double sum = 0.0;
	double precision = 0.000001;
	int k = 0;
	int sign = 1;
	double item = 1;
	do{
		sum += item;
		
		k++, sign *= -1;
		item = sign * 1.0 / (2 * k + 1);
	} while (fabs(item) >= precision);

	return sum * 4.0;
}


int main()
{
	double res = _sin(3.1415926 / 2);

	double pi = PI();

	return 0;
}