题目一：

#include<stdio.h>
#include<math.h>

int main()
{
	int n = 1;
	float sum = 0, term = 1, sign = 1;
	while (fabs(term) > 1e-4)
	{
		term = sign / n;
		sum += term;
		sign = -sign;
		n++;
	}
	printf("sum=%f", sum);
	return 0;
}

---

题目二：

#include<stdio.h>
#include<math.h>

int main()
{
	int n = 1, count = 1;
	float sum, term;
	float x;
	printf("Input x：");
	scanf_s("%f", &x);

	sum = x;
	term = x;
	while (fabs(term) > 1e-5)
	{
		term = -term * x * x / ((n + 1) * (n + 2));
		sum += term;
		n = n + 2;
		count++;
	}
	printf("sin(x)=%f,count=%d", sum, count);
	return 0;
}

---

题目三：

#include<stdio.h>
#include<math.h>
int main()
{
	int count = 0, sign = 1, n = 1;
	double sum = 0, term = 1;
	while (fabs(term) > 1e-4)
	{
		term = (float)sign / n;
		sum += term;
		sign = -sign;
		n = n + 2;
		count++;
	}
	printf("pi=%f,count=%d", 4 * sum, count);
	return 0;
}

---

题目四：

#include<stdio.h>
#include<math.h>
int main()
{
	int count=1;
	double sum = 1, term = 1;
	while (fabs(term) > 1e-5)
	{
		term = term / count;
		sum += term;
		count++;
	}
	printf("e=%f,count=%d", sum, count);
	return 0;
}