C语言计算规律题

• 寻找每一项的规律，再求和。

#include 

int main()
{
	int i,sum = 0,term;
	for (i = 1;i <= 99;i += 2)
	{
		term = i * (i + 1) * (i + 2);
		sum += term;
	}
	printf("sum=%d",sum);
	return 0;
}

1. 方法1。计算第一个值、求和、第二个值用第一个值乘以10加上第一个值。

#include 

int main()
{
	int n,a,sum = 0,term = 0;
	printf("请输入n和a的值：n");
	scanf("%d,%d",&n,&a);
	for (int i = 1;i <= n;i++)
	{
		term += a;
		sum += term;
		a *= 10;
	}
	printf("sum=%d",sum);
	return 0;
}

2. 方法2。第二个值用第一个值乘以10加上第一个值，求和。

#include 

int main(void)
{
	int n,a,term=0,sum=0;
	printf("请输入n和a的值：n");
	scanf("%d,%d",&n,&a);
	for (int i = 1;i <= n;i++)
	{
		term = term * 10 + a;
		sum += term;
	}
	printf("sum=%d",sum);
	return 0;
}

• 把握精度。

#include 

int main(void)
{
	int i = 1;
	float sign = 1;
	double sum = 0;
	while ((1.0/i) >= 1e-6 || (1.0/i) <= 1e-6)
	{
		sum += sign / i;
		i++;
		sign = -sign;
	}
	printf("sum=%lf",sum);
	return 0;
}

• 防止溢出

#include 
#include 

int main(void)
{
	int n = 1,count = 1;
	float x;
	double sum,term;
	printf("请输入x值：n");
	scanf("%f",&x);
	sum = x;
	term = x;
	do{
		term = -term * x * x / ((n + 1) * (n + 2));
		sum += term;
		n += 2;
		count++;
	}while (fabs(term) >= 1e-5);
	printf("sin(x)=%f,count=%d",sum,count);
}