大三时候实现的，关于大整数（超过long范围）加减乘除操作的头文件，并包含了实现RSA加解密的函数

#include<iostream>
#include<time.h>
#include<string.h>
using namespace std;


class BigNum{
private:
    int *num;                                        //数值
    int *yu;                                        //余数
    int n;                                            //数值位数
    int YuNum;                                        //余数位数
    bool sym;                                        //正负，true为正
public:
    BigNum(char *str){
        n = strlen(str);
        YuNum = 0;sym = true;
        num = new int[strlen(str)];
        for(int i = 0 ; i < strlen(str) ; i++)
            num[i] = str[strlen(str)-i-1]-'0';
    }
    BigNum(int A){
        int i,j;
        int a = A;
        for(i=0; a!=0; i++)
            a/=10;
        num = new int[i];
        a = A;
        for(j=0; j<i; j++){
            num[j] = a%10;
            a/=10;
        }
        n = i;
        YuNum = 0;
    }
    BigNum(bool a){
        YuNum = 0;sym = true;
        char *str = new char[256];
        cout<<"输入数以建立对象:"<<endl;
        cin>>str;
        n = strlen(str);
        num = new int[strlen(str)];
        for(int i = 0 ; i < strlen(str) ; i++)
            num[i] = str[strlen(str)-i-1]-'0';
    }
    BigNum(){
        sym = true;
        n = 0;
        YuNum = 0;
    }
    BigNum operator+(BigNum p){
        BigNum temp = BigNum();
        int i;
        if( this->sym + p.sym == 1){
            bool s;
            if(*this > p){
                s = this->sym;
                this->sym = p.sym;
                temp = *this - p;
                temp.sym = s;
            }
            else{
                s = p.sym;
                p.sym = this->sym;
                temp = p - *this;
                temp.sym = s;
            }
            return temp;
        }
        int c=0;                                                    //进位
        temp.n = max(this->n ,p.n );
        int *Num = new int[temp.n +1 ];
        for( i=0; i<min(this->n ,p.n); i++){
            Num[i]= (this->num[i] +p.num[i] +c) %10;
            c = (this->num[i]+p.num[i]+c)/10;
        }
        if(this->n > p.n)
            for( i = p.n ; i < temp.n ; i++){
                Num[i] = (this->num[i]+c)%10;
                c = (this->num[i]+c)/10;
            }
        else
            for( i=this->n;i<p.n;i++){
                Num[i] = (p.num[i]+c)%10;
                c = (p.num[i]+c)/10;
            }
        if(c>0){
            temp.n++;
            Num[temp.n-1]=c;
        }
        temp.num = new int[temp.n];
        for(int i=0;i<temp.n;i++)
            temp.num[i] = Num[i];
        return temp;
    }
    BigNum operator-(BigNum p){
        BigNum temp = BigNum();
        int i;
        if(this->sym + p.sym == 1){                            //异符号相减是两数绝对值相加，符号取减数
            bool s = this->sym;
            this->sym = p.sym;
            temp = *this + p;
            temp.sym = s;
            return temp;
        }
        if(!(*this > p)){
            temp = p - *this;                                //减法结果出现负数
            temp.sym = false;
            return temp;
        }
        int c=0;                                    //进位
        int *Num = new int[this->n];
        for( i=0;i<this->n;i++){
            if(i<p.n){
                if(this->num[i]+c>=p.num[i]){
                    Num[i] = this->num[i]+c-p.num[i];
                    c=0;
                }
                else{
                    Num[i] = this->num[i]+c+10-p.num[i];
                    c=-1;
                }
            }
            else{
                if(this->num[i]+c>=0){
                    Num[i] = this->num[i]+c;
                    c = 0;
                }
                else{
                    Num[i] = this->num[i]+c+10;
                    c = -1;
                }
            }
        }
        temp.n = this->n;
        for( i=this->n-1;Num[i]==0&&i>=0;i--)
            temp.n--;
        temp.num = new int[temp.n];
        for( i=0;i<temp.n;i++)
            temp.num[i] = Num[i];
        return temp;
    }
    BigNum operator*(BigNum p){
        int i;
        BigNum temp = BigNum();
        if(this->sym + p.sym == 1)
            temp.sym = false;
        if(this->n==0 || p.n==0)
            return temp;
        int *Num = new int[p.n+this->n+1];                        //循环中可能会用到最后一个数
        int c = 0;
        for(i=0; i < this->n+p.n; i++)
            Num[i] = 0;
        for(i=0; i < p.n+this->n; i++){
            for(int j=0; j < this->n; j++)
                for(int k=0; k < p.n; k++){
                    if(i==j+k)
                        c += this->num[j]*p.num[k];
                }
            Num[i]+=c%10;
            c=c/10;
        }
        for(i=this->n+p.n; Num[i] <= 0; )
            i--;
        temp.n=i+1;
        temp.num = new int[temp.n];
        for(i=0; i<temp.n; i++)
            temp.num[i] = Num[i];
        return temp;
    }
    bool operator> (BigNum p){                                //大于等于的效果，跟小于对立，只比较绝对值，不关心正负
        if(this->n > p.n)
            return true;
        else if(this->n < p.n)
            return false;
        else{
            for(int i=1 ; i <= p.n; i++){
                if(this->num[n-i] == p.num[n-i])
                    continue;
                else if(this->num[n-i] <= p.num[n-i])
                    return false;
                else
                    return true;
            }
            return true;
        }
    }
    BigNum operator/(BigNum p){
        BigNum temp = BigNum();
        int i,j,k;
        temp.sym = this->sym + p.sym;
        if(!(*this > p)){
            temp.n = 0;
            temp.yu = new int[this->n];
            temp.YuNum = this->n;
            for( i=0;i<this->n;i++)
                temp.yu[i] = this->num[i];
            return temp;
        }
        int *Num = new int[this->n-p.n+1];
        for( i=0;i<this->n-p.n+1;i++)                        //置零
            Num[i] = 0;
        BigNum mid = BigNum();                                    //让mid成为this的复制，在处理中要改变其中的值
        mid.n = this->n;
        mid.num = new int[mid.n];
        for( i = 0; i < mid.n; i++)
            mid.num[i] = this->num[i];
        int m = mid.n - p.n;                                    //用首位相减法，跟人手酸除法的过程相似，需要改变mid中的数值和位数，m存储低位没用到的位数
        mid.n = p.n;    mid.num += this->n - p.n;                //把mid置成跟p相同长度，开始相减，指针相应的向后移动
        for( i = this->n - p.n +1-1;i >= 0;  ){
            BigNum A = BigNum();                                //A是中间变量为了使mid的数值动态化
            while( mid > p ){
                A = mid - p;
                for( k=0; k < A.n ; k++)
                    mid.num[k] = A.num[k];
                for( k=A.n; k < mid.n; k++)
                    mid.num[k] = 0;
                Num[i] +=1;
                for( j = mid.n-1; j >= 0 ;j--,mid.n-- )                //去掉开头的零
                    if(mid.num[j] != 0)
                        break;
            }
            if( m + mid.n<p.n || m == 0 && p >mid){                                        //剩下的数总和比P小，除法完成
                temp.yu = new int[m + mid.n];
                mid.num -= m;
                for( k = 0; k < m + mid.n ; k++)
                    temp.yu[k] = mid.num[k];
                temp.YuNum = m + mid.n;
                //mid.n = this->n;
                int j = this->n - p.n + 1;
                for( ; j>0 ; j--)
                    if(Num[j-1] != 0)
                        break;
                temp.num = new int[j];
                for( k = 0;k < j ; k++ )
                    temp.num[k] = Num[k];
                temp.n = j;
                return temp;
            }
            else{
                m -= p.n - mid.n;
                mid.num -= p.n - mid.n;
                i -= p.n - mid.n;
                mid.n = p.n;
                if( m > 0 && p > mid){                //借位
                    m--;
                    i--;
                    mid.num--;
                    mid.n++;
                }
                for( k = mid.n ; mid.num[k-1] == 0 && k >= 1 ; k--)
                    mid.n--;
            }
        }
        return temp;
    }
    void display(){
        int i;
        if( sym == false )
            cout<<'-';
        for( i=0 ;i < n; i++)
            cout<<num[n-i-1];
        if(YuNum > 0){
            cout<<endl;
            for( i=0; i < YuNum; i++)
                cout<<yu[YuNum-i-1]<<' ';
        }
        cout<<endl;
    }
    static void swap(BigNum &a,BigNum &b){
        BigNum temp = a;
        a = b;
        b=temp;
    }
    static BigNum gcd(BigNum A,BigNum B){
        int i;
        BigNum temp;
        BigNum a;a = A;
        BigNum b;b = B;
        while(true){
            temp = a/b;
            if( a>b )
                BigNum::swap( a,b );
            free(b.num);
            b.n = temp.YuNum;
            b.num = new int[a.n];
            for( i=0;i < temp.YuNum; i++){
                b.num[i] = temp.yu[i];
            }
            if(  temp.YuNum==0 )
                break;
        }
        return a;
    }
    void operator=(BigNum p){
        int i;
        this->~BigNum();
        this->sym = p.sym;
        this->n = p.n;
        this->num = new int[this->n];
        for( i=0; i< p.n; i++)
            this->num[i] = p.num[i];
        this->YuNum = p.YuNum;
        this->yu = new int[this->YuNum];
        for( i=0; i< p.YuNum; i++)
            this->yu[i] = p.yu[i];
    }
    static BigNum inv(BigNum a, BigNum b){                                            //小的放在前面
        BigNum a0 = a;
        BigNum b0 = b;
        BigNum t0;
        BigNum t("1");
        BigNum s0("1");
        BigNum s;
        BigNum q = a0 /b0;
        BigNum r = a0 - (q * b0);
        BigNum temp;
        while( r > BigNum("1") ){
            temp = t0 - (q * t);
            t0 = t;
            t = temp;
            temp = s0 - (q * s);
            s0 = s;
            s = temp;
            a0 = b0;
            b0 = r;
            q = a0 /b0;
            r = a0 - (q * b0);
        }
        r = b0;
        if( s.sym == false )
            s = s + b;
        return s;
    }
    bool operator==(BigNum p){
        if( this->n == p.n ){
            for(int i=0; i < p.n; i++)
                if( this->num[i] != p.num[i] )
                    return false;
            return true;
        }
        return false;
    }
    char* toChar(){
        int i;
        char *str = new char[this->n+2];
        for(i=0; i<this->n; i++)
            str[this->n-i-1] = '0'+this->num[i];
        str[i] = '\0';
        return str;
    }
    BigNum mod(BigNum n){
        BigNum temp;
        if(!(*this> n)){
            temp.n = this->n;
            temp.num = new int[temp.n];
            for(; temp.n>0; temp.n--)
                temp.num[temp.n-1] = this->num[temp.n-1];
            temp.n = this->n;
        }
        else{
            BigNum y = *this /n;
            temp.n = y.YuNum;
            temp.num = new int[temp.n];
            for( ; temp.n>0; temp.n--)
                temp.num[temp.n-1] = y.yu[temp.n-1];
            temp.n = y.YuNum;
        }
        return temp;
    }
    static BigNum Square_and_Multiply(BigNum X, BigNum C, BigNum N){            //幂模运算z = x^c(mod n)
        int i;
        BigNum x = X;BigNum c = C;BigNum n = N;
        BigNum two("2");
        for(i=0; c.n>0; i++)
            c = c /two;
        bool *bol = new bool[i];
        c = C;
        for(i=0; c.n>0; i++){
            c = c /two;
            if(c.YuNum > 0)
                bol[i] = 1;
            else
                bol[i] = 0;
        }
        BigNum z("1");
        for( ; i >0; i--){
            z = (z*z).mod(n);                        //只返回正数
            if(bol[i-1] == 1)
                z = (z*x).mod(n);
        }
        return z;
    }
    static bool Miller_Rabin(BigNum X){                //Miller Rabin算法判断大数X是否为素数，是素数返回true
        int i,k;
        BigNum x = X;
        BigNum two("2");
        x = x - BigNum("1");
        for(k=0; x.YuNum==0; k++){
            x = x /two;
        }
        BigNum m = x*two + BigNum("1");
        k= k- 1;
        BigNum b = Square_and_Multiply(BigNum("2"),m,X);
        x = X - BigNum("1");
        if( b==BigNum("1"))    return true;
        for(i=0; i<k; i++){
            if( b==x)
                return true;
            else
                b = Square_and_Multiply(b,two,X);
        }
        return false;
    }
    static BigNum create_prime(int m){
        int i;
        BigNum num("1");
        BigNum one("1");
        BigNum two("2");
        srand(time(0));
        for(i=0; i<m-1; i++){
            num = num* two + BigNum(rand()).mod(two);
        }
        BigNum temp;
        while(true){
            temp = num;
            for(i=1; temp>two; i++)
                temp = temp /two;
            if(Miller_Rabin(num)&&i==m)
                return num;
            else if(i>m){
                num = create_prime(m);
                return num;
            }
            else
                num = num+ two;
        }
    }
};

以上是BigNum.h的源码，下面是应用范例：

#include"BigNum.h"
#include<fstream>

void main(){
    char *str = new char[256];
    cout<<"输入密钥";cin>>str;
    BigNum c = BigNum(str);
    cout<<"输入n";cin>>str;
    BigNum n = BigNum(str);
    ifstream in("data.txt");
    ofstream out("result.txt");
    BigNum x;
    BigNum y;
    char g;
    while(!in.eof()){
        in.get(str,100,' ');
        if(!(in.eof()))
            in.get(g);
        x = BigNum( str );
        y = BigNum::Square_and_Multiply(x, c, n);
        out<<y.toChar()<<' ';
        y.display();
    }
    /*string ss;
    BigNum data;
    BigNum yu;                                                //余数
    BigNum sh;                                                //商
    BigNum one("1");
    while( !in.eof() ){
        in>>num;
        sh = BigNum("1");
        data = BigNum(num);
        for( BigNum i = BigNum("1") ; k >i; i =i +one){
            sh = sh * data;
            yu = sh / n;
            //free(temp->num);
            sh.~BigNum();
            sh =BigNum();
            sh.n =yu.YuNum;
            sh.num = new int[sh.n];
            for(int j = 0; j < yu.YuNum ; j++){
                sh.num[j] = yu.yu[j];
            }
            //free(temp->yu);temp->YuNum =0;
        }
        sh.display();
        out<<sh.toChar()<<' ';
    }*/
    in.close();
    out.close();
    getchar();
    getchar();
}

其中需要文件data.txt（对其中的数据进行加密）：

599973434 2978448901 1049145034