【算法】求n!，求1!+2!+...+(n-1)!+n!

1、求阶乘 n！

int main() {

	int i, n, ret;

	printf("输入n的值：");
	scanf("%d", &n);
	
	ret = 1;
	for (i = 1; i <= n; i++) {

		ret = ret * i;
	}
	printf("n!= %d",ret);
	
	return 0;
}

2、求阶乘之和 n!+(n-1)!+...+1!

int main() {

	int i, j, n, ret, sum;

	printf("输入的n是：");
	scanf("%d", &n);

	sum = 0;
	for (j = 1; j <= n; j++) {

		ret = 1;
		for (i = 1; i <= j; i++) {

			ret = ret * i;
		}
		sum = sum + ret;
	}

	printf("n!= %d\n", ret);
	printf("n!+(n-1)!+...+1!= %d\n", sum);

	return 0;
}

性能优化后代码，

int main() {

	int i, n, ret, sum;

	printf("输入的n是：");
	scanf("%d", &n);

	ret = 1;
	sum = 0;
	for (i = 1; i <= n; i++) {

		ret = ret * i;
		sum = sum + ret;
	}

	printf("n!= %d\n", ret);
	printf("n!+(n-1)!+...+1!= %d\n", sum);

	return 0;
}

输出结果：