大数乘法，大数加法，大数减法

#include <iostream>

#include<cstring>

using namespace std;

class MData

{

 private:

    int n,m;

    char *str1,*str2;

 public:

    char *mul();//乘法

    char *add();//加法

    char *sub();//减法

    char *div();//除法

    MData();

    MData(const char *s1,const char * s2);

    void init(const char *s1,const char * s2);

    ~MData();

};

MData::MData()

{

    str1=nullptr;

    str2 = nullptr;

    n = 0;

    m = 0;

}

MData::MData(const char *s1, const char *s2)

{

    n = (int)strlen(s1);

    m = (int)strlen(s2);

    str1 = new char[n+1]{''};

    str2 = new char[m+1]{''};

    strcpy(this->str1,s1);

    strcpy(this->str2,s2);

}

void MData::init(const char *s1,s2);

}

MData::~MData()

{

    if(str1!=nullptr)

        delete[] str1;

    if(str2!=nullptr)

        delete[] str2;

}

char* MData::mul()//乘法

{

    int *s = new int[n+m];

    memset(s,0,sizeof(int)*(n+m));

    for(int i = 0;i<n;i++)

        for(int k = 0;k<m;k++)

        {

            s[i+k+1] += (str1[i]-'0')*(str2[k]-'0');

        }

    for(int i = n+m-1;i>=0;i--)

    {

        if(s[i]>=10)

        {

            s[i-1] += s[i]/10;

            s[i] %= 10;

        }

    }

    int i = 0;

    while(s[i] == 0)

    {

        i++;

        if(i == n+m)

            return "0";

    }

    char *sum = new char[n+m-i+1]{''};

    int k = 0;

    int kn = n+m-i+1;

    for(;k<kn&&i<n+m;k++,i++)

    {

        sum[k] = s[i]+'0';

    }

    sum[k] = '';

    delete[] s;

    return sum;

}

char *MData::add()//加法

{

    int *s,temp;

    if(n > m)

    {

         temp = n;

         s = new int[n+1];

         memset(s,sizeof(int)*(n+1));

         for(int i = 0;i<n;i++)

         {

             if(i >= n-m)

                s[i+1] = (str1[i]-'0')+(str2[i-(n-m)]-'0');

             else

                 s[i+1] = str1[i]-'0';

         }

    }

    else

    {

        temp = m;

        s = new int[m+1];

        memset(s,sizeof(int)*(m+1));

        for(int i = 0;i<m;i++)

        {

            if(i >= m-n)

               s[i+1] = (str2[i]-'0')+(str1[i-(m-n)]-'0');

            else

                s[i+1] = str2[i]-'0';

        }

    }

    for(int i = temp;i>=0;i--)

    {

        if(s[i]>=10)

        {

            s[i-1] += s[i]/10;

            s[i] %= 10;

        }

    }

    int i = 0;

    while(s[i] == 0)

    {

        i++;

        if(i == temp+1)

            return "0";

    }

    char *sum = new char[(temp+1)-i+1]{''};

    int k = 0;

    int kn = (temp+1)-i+1;

    for(;k<kn&&i<temp+1;k++,i++)

    {

        sum[k] = s[i]+'0';

    }

    sum[k] = '';

    delete[] s;

    return sum;

}

char *MData::sub()

{

    int *s,temp;

    bool bt = false;

    if(n >= m)

    {

        s = new int[n+1];

        temp = n;

        memset(s,sizeof(int)*(n+1));

        if(n > m)

        {

            for(int i = 0;i < n;i++)

            {

                if(i >= n-m)

                    s[i+1] = (str1[i]-'0')-(str2[i-(n-m)]-'0');

                else

                    s[i+1] = str1[i]-'0';

            }

        }

        else

        {

            if(strcmp(str1,str2)>0)

            {

                for(int i = 0;i < n;i++)

                {

                    s[i+1] = (str1[i]-'0')-(str2[i]-'0');

                }

            }

            else

            {

                bt = true;

                for(int i = 0;i < n;i++)

                {

                    s[i+1] = (str2[i]-'0')-(str1[i]-'0');

                }

            }

        }

    }

    else

    {

        bt = true;

        s= new int[m+1];

        temp = m;

        memset(s,sizeof(int)*(m+1));

        for(int i = 0;i<m;i++)

        {

            if(i >= m-n)

                s[i+1] = (str2[i]-'0')-(str1[i-(m-n)]-'0');

            else

                s[i+1] = str2[i]-'0';

        }

    }

    for(int i = temp;i>=0;i--)

    {

        if(s[i] < 0)

        {

            s[i-1] -= 1;

            s[i] += 10;

        }

    }

    int i = 0;

    while(s[i] == 0)

    {

        i++;

        if(i == n+1)

        {

            return "0";

        }

    }

    char *sum;

    if(bt)

    {

        sum = new char[(temp+1)-(i-1)+1]{''};

        int k = 0;

        int kn = (temp+1)-i+1;

        for(;k<kn&&i<temp+1;k++,i++)

        {

           if(k == 0)

               sum[k] = '-';

           sum[k+1] = s[i]+'0';

        }

        sum[k+1] = '';

    }

    else

    {

        sum = new char[(temp+1)-i+1]{''};

        int k = 0;

        int kn = (temp+1)-i+1;

        for(;k<kn&&i<temp+1;k++,i++)

        {

           sum[k] = s[i]+'0';

        }

        sum[k] = '';

    }

    delete[] s;

    return sum;

}

char *MData::div()

{

    if(n < m)

        return "0";

    else

    {

        if(n == m)

        {

            if(strcmp(str1,str2) < 0)

                return "0";

            else

            {

                int i = 0;

                char *st = this->sub();

                while(st[0]!='-')

                {

                    i++;

                    strcpy(str1,st);

                    st = this->sub();

                }

                char *str = new char[2]{0};

                str[0] = i+'0';

                str[1] = '';

                return str;

            }

        }

        else

        {

            int *s = new int[n];

            for(int i = 0;i<n;i++)

                s[i] = 0;

            int i = 0;

            char *str = new char[m]{0};

            str = strncpy(str,str1,1);

            str[1] = '';

            char *tp = str1+1;

            char *temp = str1;

            str1 = str;

            while(i<n)

            {

                if(strlen(str1) < m ||

                        (strcmp(str1,str2)<0 && strlen(str1) == m))

                {

                    strncpy(str,tp,1);

                    str[1] = '';

                    str1 = strcat(str1,str);

                    tp++;

                    i++;

                }

                else

                {

                    s[i]++;

                    str1 = this->sub();

                }

                if(i == n)

                {

                    break;

                }

            }

            for(int mm = n-1;mm >= 0;mm--)

            {

                if(s[mm] >= 10)

                {

                    s[mm-1] += s[mm]/10;

                    s[mm] %= 10;

                }

            }

            int nn = 0;

            while(s[nn] == 0)

            {

                nn++;

                if(nn == n)

                    return "0";

            }

            char *strchar = new char[n+1 -nn];

            memset(strchar,sizeof(char)*(n+1-nn));

            int k = 0;

            for(;k<n && nn < n;k++,nn++)

            {

                strchar[k] = s[nn]+'0';

            }

            strchar[k] = '';

            delete[] temp;

            return strchar;

        }

    }

}

int main()

{

    int i = 0;

    while(i<100)

    {

        i++;

        char *str1=new char[10000]{''},*str2=new char[10000]{''};

        cin>>str1;

        cin>>str2;

        MData sk(str1,str2);

        char *mul = sk.mul();//乘法

        cout << "1:"<< mul << endl;

        char *add = sk.add();//加法

        cout<<"2:" << add<<endl;

        char *sub = sk.sub();//减法

        cout<<"3:"<< sub <<endl;

        //char *div = sk.div();//除法

        //cout<<"4:"<<div<<endl<<endl;

        if(i == 100)

        {

            delete[]str1;

            delete[]str2;

        }

    }

    return 0;

}
大数除法还有问题，没有时间去完善，如果你完善了，请评论并回复代码哈，谢谢了

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