高精度模板 仅加法与减法

高精度加法

#include<iostream>
using namespace std;

string str1, str2;

int main(){
    cin >> str1 >> str2;
    string str;
    int a1 = str1.length();
    int a2 = str2.length();
    if(a1>a2){
        for (int i = a2; i < a1;i++){
            str2 = "0" + str2;
        }
    }else{
        for (int i = a1; i < a2;i++){
            str1 = "0" + str1;
        }
    }
    cout << str1 << endl;
    cout << str2 << endl;
    int m = str1.length();
    int cf = 0;
    int item;
    for (int i = m - 1; i >= 0;i--){
        item = (str1[i] - '0') + (str2[i] - '0')+cf;
        cf = item / 10;
        item %= 10;
        str = char(item + '0') + str;
    }
    if(cf!=0){
        str = char(cf + '0') + str;
    }
    cout << str;
}

高精度减法

#include<iostream>
using namespace std;

int main(){
    string a, b;
    string str;
    cin >> a >> b;
    int cf = 0;
    int item = a.length() - b.length();
    int j = b.length() - 1;
    for (; j >= 0;j--){
        if(a[item+j]<(b[j]+cf)){
            str = char(a[item + j] - b[j] - cf + 10 + '0') + str;
            cf = 1;
        }else{
            str = char(a[item + j] - b[j] - cf + '0' ) + str;
            cf = 0;
        }
    }
    for (int i = item - 1; i >= 0 ;i--){
        if(a[i]-cf<'0'){
            str = char(a[i]- cf + 10) + str;
            cf = 1;
        }else{
            str = char(a[i] - cf) + str;
            cf = 0;
        }
    }
    cout << str;
}