直接当unsigned int用，还可以直接查询从右往左起的任意一位数只不过初始化不同，具体看代码

代码：

#include <iostream>
#include "longint.h"
using namespace std;
/*
支持操作：
--------------------------------a和b为longint或int----------------------------------------
01.cin
02.cout
03.a+b
04.a-b
05.a*b
06.a/b
07.a%b
08.a += b
09.a -= b
10.a *= b
11.a /= b
12.a %= b
13.a++
14.b++
15.++a
16.++b
17.a > b
18.a < b
19.a >= b
20.a <= b
21.a == b
22.a != b
23.pow (a,b)
24.fact (a)
*/
int main () {
    cin >> a >> b;
    cout << a+b << endl << a-b << endl << a*b << endl << a/b << endl << a%b << endl;
    return 0;
}

$longint.h:$

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
struct longint {
    int num[10010];
    int len;
    longint (int a = 0) {
        len = 1;
        memset (num,0,sizeof (num));
        int l = 0;
        while (a) {
            num[++l] = a%10;
            a /= 10;
        }
        len = l;
    }
    operator bool () {
        return len == 1 && num[1] == 0;
    }
    longint (int n[10010],int l = 1) {
        for (int i = 1;i < l;i++) num[i] = n[i];
        len = l;
    }
    int size () {
        return len;
    }
    void operator = (longint a) {
        for (int i = 1;i <= a.size ();i++) num[i] = a[i];
        len = a.len;
    }
    int &operator [] (int x) {
        return num[x];
    }
    longint & operator ++ () {
        longint a;
        for (int i = 1;i <= len;i++) a[i] = num[i];
        a.len = len;
        longint b (1);
        int l = max (len,b.len);
        memset (num,0,sizeof (num));
        for (int i = 1;i <= l;i++) {
            num[i] += a[i]+b[i];
            num[i+1] += num[i]/10;
            num[i] %= 10;
        }
        if (num[l+1] > 0) l++;
        len = l;
        return *this;
    }
    longint operator ++ (int) {
        longint a;
        for (int i = 1;i <= len;i++) a[i] = num[i];
        a.len = len;
        longint b (1);
        int l = max (a.len,b.len);
        for (int i = 1;i <= l;i++) {
            num[i] += a.num[i]+b.num[i];
            num[i+1] += num[i]/10;
            num[i] %= 10;
        }
        if (num[l+1] > 0) l++;
        len = l;
        return a;
    }
    longint & operator -- () {
        longint a;
        for (int i = 1;i <= len;i++) a[i] = num[i];
        a.len = len;
        longint b (1);
        int l = max (len,b.len);
        for (int i = 1;i <= l;i++) {
            if (a[i] < b[i]) {
                num[i] += 10;
                num[i+1]--;
            }
            num[i] -= b[i];
        }
        while (num[l] == 0 && l > 1) l--;
        len = l;
        return *this;
    }
    longint operator -- (int) {
        longint a;
        for (int i = 1;i <= len;i++) a[i] = num[i];
        a.len = len;
        longint b (1);
        int l = max (a.len,b.len);
        for (int i = 1;i <= l;i++) {
            if (a[i] < b[i]) {
                num[i] += 10;
                num[i+1]--;
            }
            num[i] -= b[i];
        }
        while (num[l] == 0 && l > 1) l--;
        len = l;
        return a;
    }
};
longint chg (int a) {
    longint ans;
    if (a == 0) return ans;
    int len = 0;
    while (a) {
        ans.num[++len] = a%10;
        a /= 10;
    }
    ans.len = len;
    return ans;
}
int chg (longint a) {
    int ans = 0;
    for (int i = a.size ();i >= 1;i--) ans = ans*10+a[i];
    return ans;
}
longint chg (string s) {
    longint a;
    int len = s.size ();
    for (int i = 1;i <= len;i++) {
        a.num[i] = s[len-i]-'0';
    }
    a.len = len;
    return a;
}
bool operator < (longint a,longint b) {
    if (a.len != b.len) return a.len < b.len;
    for (int i = a.len;i >= 1;i--) {
        if (a[i] != b[i]) return a[i] < b[i];
    }
    return false;
}
bool operator < (longint a,int b) {return a < chg (b);}
bool operator < (int a,longint b) {return chg (a) < b;}
bool operator > (longint a,longint b) {
    if (a.len != b.len) return a.len > b.len;
    for (int i = a.len;i >= 1;i--) {
        if (a[i] != b[i]) return a[i] > b[i];
    }
    return false;
}
bool operator > (longint a,int b) {return a > chg (b);}
bool operator > (int a,longint b) {return chg (a) > b;}
bool operator <= (longint a,longint b) {
    if (a.len != b.len) return a.len <= b.len;
    for (int i = a.len;i >= 1;i--) {
        if (a[i] != b[i]) return a[i] <= b[i];
    }
    return true;
}
bool operator <= (longint a,int b) {return a <= chg (b);}
bool operator <= (int a,longint b) {return chg (a) <= b;}
bool operator >= (longint a,longint b) {
    if (a.len != b.len) return a.len > b.len;
    for (int i = a.len;i >= 1;i--) {
        if (a[i] != b[i]) return a[i] >= b[i];
    }
    return true;
}
bool operator >= (longint a,int b) {return a >= chg (b);}
bool operator >= (int a,longint b) {return chg (a) >= b;}
bool operator == (longint a,longint b) {
    if (a.len != b.len) return false;
    for (int i = a.len;i >= 1;i--) {
        if (a[i] != b[i]) return false;
    }
    return true;
}
bool operator == (longint a,int b) {return a == chg (b);}
bool operator == (int a,longint b) {return chg (a) == b;}
bool operator != (longint a,longint b) {
    if (a.len != b.len) return true;
    for (int i = a.len;i >= 1;i--) {
        if (a[i] != b[i]) return true;
    }
    return false;
}
bool operator != (longint a,int b) {return a != chg (b);}
bool operator != (int a,longint b) {return chg (a) != b;}
istream &operator >> (istream &in,longint &a) {
    string s;
    in >> s;
    a = chg (s);
    return in;
}
ostream &operator << (ostream &out,longint a) {
    for (int i = a.size ();i >= 1;i--) out << a[i];
    return out;
}
longint operator + (longint a,longint b) {
    longint c;
    int len = max (a.len,b.len);
    for (int i = 1;i <= len;i++) {
        c.num[i] += a.num[i]+b.num[i];
        c.num[i+1] += c.num[i]/10;
        c.num[i] %= 10;
    }
    if (c.num[len+1] > 0) len++;
    c.len = len;
    return c;
}
longint operator + (longint a,int b) {return a+chg (b);}
longint operator + (int a,longint b) {return chg (a)+b;}
longint operator - (longint a,longint b) {
    if (a == b) return chg (0);
    int len = a.len;
    for (int i = 1;i <= len;i++) {
        if (a[i] < b[i]) {
            a[i] += 10;
            a[i+1]--;
        }
        a[i] -= b[i];
    }
    while (a.num[len] == 0 && len > 1) len--;
    a.len = len;
    return a;
}
longint operator - (longint a,int b) {return a-chg (b);}
longint operator - (int a,longint b) {return chg (a)-b;}
longint operator * (longint a,longint b) {
    longint c;
    int len = a.len+b.len;
    for (int i = 1;i <= a.len;i++) {
        for (int j = 1;j <= b.len;j++) {
            c.num[i+j-1] += a.num[i]*b.num[j];
            c.num[i+j] += c.num[i+j-1]/10;
            c.num[i+j-1] %= 10;
        }
    }
    while (c.num[len] == 0 && len > 1) len--;
    c.len = len;
    return c;
}
longint operator * (longint a,int b) {return a*chg (b);}
longint operator * (int a,longint b) {return chg (a)*b;}
void numcpy (longint a,longint &b,int idx) {
    for (int i = 1;i <= a.size ();i++) b[i+idx-1] = a[i];
    b.len = a.size ()+idx-1;
}
longint operator / (longint a,longint b) {
    longint c;
    int len = a.size ()-b.size ()+1;
    for (int i = len;i >= 1;i--) {
        longint tmp;
        numcpy (b,tmp,i);
        while (a >= tmp) {
            c[i]++;
            a = a-tmp;
        }
    }
    while (len > 1 && c[len] == 0) len--;
    c.len = len;
    return c;
}
longint operator / (int a,longint b) {return chg (a)/b;}
longint operator / (longint a,int b) {return a/chg (b);}
longint operator % (longint a,longint b) {
    longint c;
    int len = a.size ()-b.size ()+1;
    for (int i = len;i >= 1;i--) {
        longint tmp;
        numcpy (b,tmp,i);
        while (a >= tmp) {
            c[i]++;
            a = a-tmp;
        }
    }
    return a;
}
longint operator % (int a,longint b) {return chg (a)%b;}
longint operator % (longint a,int b) {return a%chg (b);}
void operator += (longint &a,longint b) {a = a+b;}
void operator += (longint &a,int b) {a = a+chg (b);}
void operator -= (longint &a,longint b) {a = a-b;}
void operator -= (longint &a,int b) {a = a-chg (b);}
void operator *= (longint &a,longint b) {a = a*b;}
void operator *= (longint &a,int b) {a = a*chg (b);}
void operator /= (longint &a,longint b) {a = a/b;}
void operator /= (longint &a,int b) {a = a/chg (b);}
void operator %= (longint &a,longint b) {a = a%b;}
void operator %= (longint &a,int b) {a = a%chg (b);}
longint max (longint a,longint b) {return a < b ? b : a;}
longint min (longint a,longint b) {return a > b ? b : a;}
longint fact (longint a) {
    longint ans = chg (1);
    while (a > 0) {
        ans *= a;
        a--;
    }
    return ans;
}
longint pow (longint a,longint b) {
    longint ans = chg (1);
    while (b) {
        if (b & 1) ans *= a;
        a *= a;
        b /= 2;
    }
    return ans;
}
longint pow (int a,longint b) {return pow (chg (a),b);}
longint pow (longint a,int b) {return pow (a,chg (b));}