高精度运算——加减乘除阶乘

加法

#include<iostream>
#include<string>
#include<algorithm>
using namespace std;

int main() {
   
	string a, b;
	int i = 0, j;
	int f = 0;//是否产生进位
	int ans[510];
	cin >> a >> b;
	reverse(a.begin(), a.end());
	reverse(b.begin(), b.end());

	string temp;
	//保证大数a的长度>=b的长度
	if (a.length() < b.length()) {
   
		temp = a;
		a = b;
		b = temp;
	}
	for (i = 0; i < b.length(); i++) {
   
		int temp = (a[i] - '0') + (b[i] - '0') + f;
		ans[i] = temp % 10;
		if (temp >= 10) {
   
			f = 1;
		}
		else {
   
			f = 0;
		}
	}
	if (a.length() > b.length()) {
   
		while (i < a.length()) {
   
			int temp = (a[i] - '0') + f;
			ans[i] = temp % 10;
			if (temp >= 10) {
   
				f = 1;
			}
			else {
   
				f = 0;
			}
			i++;
		}
	}
	if (f == 1) {
   
		cout << f;
	}
	for (j = i - 1; j >= 0; j--) {
   
		cout << ans[j];
	}
	return 0;
}

减法

#include<iostream>
#include<string>
#include<algorithm>

using namespace std;

#define maxsize 10100
//比较大小   1:a大  2:b大
int compare(string a, string b) {
   
	int flag = 0;
	if (a.length() > b.length()) {
   
		return 1;
	}
	else if(a.length() < b.length()){
   
		return 2;
	}
	else {
   
		//长度相等，未逆转，直接比较，低位即数值高位
		for (int i = 0; i < a.length(); i++) {
   
			if (a[i] > b[i]) {
   
				flag = 1;
				return 1;
			}
			else if (b[i] > a[i]) {
   
				flag = 1;
				return 2;
			}
		}
	}
	if (flag == 0) {
   
		return 0;//相等
	}
}
int main() {
   
	string a, b;
	int i = 0, j;
	int f = 0;//是否产生借位
	int ans[maxsize];

	cin >> a >> b;
	int c = compare