大数相加和大数相乘以及打印从1到最大的n位数

string add(string a, string b){
    int nlength;
    int diff;
    if (a.size() > b.size()){
        nlength = a.size();
        diff = a.size() - b.size();
        b.insert(b.begin(), diff, '');
        //cout << b << endl;
    }
    else{
        nlength = b.size();
        diff = b.size() - a.size();
        a.insert(a.begin(), diff, '');
        //cout << a << endl;
    }
    //cout << a << endl;
    //cout << b << endl;
    //cout << c << endl;
    int takeover = ;
    for (int i = nlength - ; i >= ; i--){
        int temp = a[i]-'' + b[i] - '' + takeover;
        cout << a[i] << " " << b[i] << endl;
        cout << temp << endl;
        if (temp >= ){
            takeover = ;
            b[i] = temp + '' - ;

            //cout << c[j] << endl;
        }
        else{
            b[i] = temp + '';
            takeover = ;

        }
    }
    //cout << takeover<<" " << j << endl;
    if (takeover == )b = '' + b;
    return b;
}

void print(string str){
    int count = ;
    for (int i = ; i < str.size(); i++){
        if (str[i] == '')count++;
        else
            break;
    }
    cout << str.substr(count, str.size() - count) << endl;;
}

注：char a='9'；

int b=a-'0';

a的范围只能是0到9

better：

一位一位相加，然后算和算进位，最后根据进位情况看需不需要补一个高位

string addStrings(string num1, string num2) {
       string res = "";
        int m = num1.size(), n = num2.size(), i = m - , j = n - , carry = ;
        while (i >=  || j >= ) {
            int a = i >=  ? num1[i--] - '' : ;
            int b = j >=  ? num2[j--] - '' : ;
            int sum = a + b + carry;
            res.insert(res.begin(), sum %  + '');
            carry = sum / ;
        }
        return carry ? "" + res : res;
    }

---

大数相乘

class Solution {
public:
    string multiply(string num1, string num2) {
        int n=num1.size();
        int m=num2.size();
        vector<int>temp(n+m,);//一个m位和n位数相乘得到的数最多是n+m位
        for(int i=n-;i>=;i--){

            for(int j=m-;j>=;j--){
                 temp[i+j+]+=(num1[i]-'')*(num2[j]-'');
            }
        }
        int bi=;
        for(int i=temp.size()-;i>=;i--){
            temp[i]=temp[i]+bi;
            bi=temp[i]/;
            temp[i]=temp[i]%;
        }
        int i = ;
        while (temp[i] == )i++;//跳过前面多余的0
        if(i>=temp.size())return "";
        string res="";
        for(;i<temp.size();i++){
            res+=temp[i]+'';
        }

        return res;
    }
};

---

打印从1到最大n位数

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

bool stop(string &str){
    bool stop = false;
    int i = str.size() - ;
    int carry = ;
    while (i >= ){
        int tmp = str[i] - '' + carry;
        if (i == str.size() - )tmp++;
        if (tmp >=){
            if (i == ){
                stop = true;
            }
            else{
                str[i] = tmp %  + '';
                carry = tmp / ;
                i--;
            }

        }
        else{
            str[i] = tmp + '';
            break;
        }
    }
    return stop;
}

void print(string &str){
    bool flag = false;
    string res;
    for (int i = ; i < str.size(); i++){
        if (str[i] == ''&&flag == false)continue;
        else if (str[i] != ''&&flag == false){
            flag = true;
            res.push_back(str[i]);
        }
        else{
            res.push_back(str[i]);
        }
    }
    cout << res << endl;
}
void PrintNumber(int n){
    string res(n,'');
    while (!stop(res)){
        print(res);
    }
}
int main(){
    int n = ;
    PrintNumber(n);
    system("pause");
    return ;
}