C++实现大数乘法算法代码

复制代码 代码如下:

//大数乘法算法

#include<iostream>

#include<string>

#include<cstring>

using namespace std;

int main()

{

string num1,num2;

cin >> num1 >> num2;

//cout << num1.size() << " " << num2.size() << endl;

const char* n1;

const char* n2;

if (num1.size() < num2.size())

{

n1 = num2.c_str();

n2 = num1.c_str();

}

else

{

n1 = num1.c_str();

n2 = num2.c_str();

}

char* n = new char[strlen(n1)+strlen(n2)+1];

for (unsigned int i = 0; i < strlen(n1)+strlen(n2); i++)

n[i] = '0';

n[strlen(n1)+strlen(n2)]='';

//cout << strlen(n) << endl;

int count = 0,flag = 0;

for (int i = strlen(n1)-1; i >= 0; i--)

{

flag++;

int x1 = n1[i]-'0';

//cout << "n1["<< i << "]为：" << x1 << endl;

char carry = '0';

for (int j = strlen(n2)-1; j >= 0; j--)

{

int x2 = n2[j]-'0';

//cout << "n2["<< j << "]为：" << x2 << endl;

//cout << "当前位未改变前值为: " << n[count] << endl;

int sum = x1*x2 + (carry-'0') + n[count]-'0';

//cout << "sum is " << sum << endl;

n[count++] = (sum % 10)+'0';

carry = (sum / 10)+'0';

//cout << "当前位的值为: " << n[count-1] << endl;

//cout << "carry的值为：" << carry << endl;

}

if (carry != '0')

{

n[count] = carry;

count = flag;

//cout << "当前位的值为: " << n[count] << endl;

}

else

count = flag;

}

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

{

if ((i == strlen(n)-1)&&(n[i] == '0'))

continue;

cout << n[i];

}

cout << endl;

delete[]n;

system("pause");

return 0;

}

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