大数乘法，大数加法，大数减法

#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]{'\0'};

str2 = new char[m+1]{'\0'};

strcpy(this->str1,s1);

strcpy(this->str2,s2);

}

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

{

n = (int)strlen(s1);

m = (int)strlen(s2);

str1 = new char[n+1]{'\0'};

str2 = new char[m+1]{'\0'};

strcpy(this->str1,s1);

strcpy(this->str2,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]{'\0'};

int k = 0;

int kn = n+m-i+1;

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

{

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

}

sum[k] = '\0';

delete[] s;

return sum;

}

char *MData::add()//加法

{

int *s,temp;

if(n > m)

{

temp = n;

s = new int[n+1];

memset(s,0,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,0,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]{'\0'};

int k = 0;

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

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

{

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

}

sum[k] = '\0';

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,0,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,0,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]{'\0'};

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] = '\0';

}

else

{

sum = new char[(temp+1)-i+1]{'\0'};

int k = 0;

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

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

{

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

}

sum[k] = '\0';

}

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] = '\0';

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] = '\0';

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] = '\0';

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

    int k = 0;

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

{

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

}

strchar[k] = '\0';

delete[] temp;

return strchar;

}

}

}

int main()

{

int i = 0;

while(i<100)

{

i++;

char *str1=new char[10000]{'\0'},*str2=new char[10000]{'\0'};

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