CPP 大数相乘法

#include <iostream>
#include <string>


using namespace std;


void largeMul(const char *a,const char *b);


int main()
{

string num1,num2; ? ? // 初始状态用string来存储大数

cout << "请输入两个大数： " << endl;
cin >> num1 >> num2;

const char *p1 = num1.c_str(); ? ?// 将string转为 const char *
const char *p2 = num2.c_str(); ? ?// 将string转为 const char *
largeMul(p1,p2);

system("pause");
return 0;

}


void largeMul(const char *numX,const char *numY)
{

int i,j,lengthX,lengthY,*s;

lengthX = strlen(numX);
lengthY = strlen(numY);

s = (int *)malloc(sizeof(int)*(lengthX + lengthY)); ? //分配存储空间
for (i = 0; i < lengthX + lengthY; i++)
{

s[i] = 0; ? ? ?// 每个元素赋初值0

}

for (i = 0; i < lengthX; i++)
{

for (j = 0; j < lengthY; j++)

{

s[i + j + 1] += (numX[i] - '0')*(numY[j] - '0');

}

}

for (i = lengthX + lengthY - 1; i >= 0; i--) ? ? ? ?// 这里实现进位操作
{

if (s[i] >= 10)

{

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

s[i] %= 10;

}

}

char *c = (char *)malloc((lengthX + lengthY)*sizeof(char)); ?//分配字符数组空间，因为它比int数组省！

i = 0;

while (s[i] == 0)
{

i++; ? // 跳过头部0元素

}

for (j = 0; i < lengthX + lengthY; i++,j++)
{

c[j] = s[i] + '0';

}

c[j] = '';

for (i = 0; i < lengthX + lengthY; i++)
{

cout << c[i];

} cout << endl; free(s);

}