高精度算法

1.高精度加法

字符串输入，数组存储

#include<iostream>
#include<string>
#include<algorithm>
#include<cstring>
using namespace std;
int main()
{
	string s1, s2;                               //用字符串输入大数
	int a[505], b[505],c[505];                   //用数组储存大数每一位上的数字
	memset(c, 0, sizeof(c));
	memset(b, 0, sizeof(b));
	memset(a, 0, sizeof(a));
	cin >> s1 >> s2;
	for (int i = 0; i < s1.size(); i++) 
		a[i] = s1[s1.size() - i - 1] - '0';
	for (int i = 0; i < s2.size(); i++)
		b[i] = s2[s2.size() - i - 1] - '0';
	int cnt = max(s1.size(), s2.size()) ;
	for (int i = 0; i <=cnt; i++)                 //核心算法
	{
		c[i] = a[i] + b[i]+c[i];
		c[i + 1] = c[i] / 10;
		c[i] = c[i] % 10;
	}
	if (c[cnt] == 0L && cnt > 0) cnt--;           //若最高位有进位，则不管，否则把前导0删除
	for (int i = cnt ; i >= 0; i--)
		cout << c[i];
	return 0;
}

2.高精度减法

字符串输入，数组存储

需要判断正负

//高精度减法
//数量级小于10的500次方
#include<iostream>
#include<string>
#include<algorithm>
#include<cstring>
using namespace std;
int main()
{
	string s1, s2;                               //用字符串输入大数
	int a[505], b[505], c[505];                   //用数组储存大数每一位上的数字
	memset(c, 0, sizeof(c));
	memset(b, 0, sizeof(b));
	memset(a, 0, sizeof(a));
	cin >> s1 >> s2;
	int flag = 0;
	if (s1.size()<s2.size()||(s1.size()==s2.size()&&s1<s2))      //判断两个数字谁大
	{                                                            //长度小的和长度相同但字典序小的 需要交换
		flag = 1;
		string t = s1;
		s1 = s2;
		s2 = t;
	}
	for (int i = 0; i < s1.size(); i++)
		a[i] = s1[s1.size() - i - 1] - '0';
	for (int i = 0; i < s2.size(); i++)
		b[i] = s2[s2.size() - i - 1] - '0';
	int cnt = max(s1.size(), s2.size());
	for (int i = 0; i <= cnt; i++)             //核心算法
	{
		if (a[i] < b[i])
		{
			a[i + 1]--;
			a[i] += 10;
		}
		c[i] = a[i] - b[i];
	}
	while (c[cnt] == 0 && cnt > 0) cnt--;
	if (flag == 1)                    //若是负数，直接输出负号
		cout << '-';
	for (int i = cnt; i >= 0; i--)
		cout << c[i];
	return 0;
}