大數-乘法

/*首先通過字符串數組獲取數字，再將字符串數組的數字轉化成整數，再參與乘法計算*/


#include <iostream> 
#include <algorithm>
#include <string>
using namespace std;
#define MAX 1000


char ca[MAX];
char cb[MAX];
int a[MAX];
int b[MAX];
int c[MAX];

void output(int m, int n)
{
for (int i = 0; i < m; i++) cout << a[i];
cout << " X ";
for (int i = 0; i < n; i++) cout << b[i];
cout << "=";
////////////////////////////////////////////
int flag = 1;
for (int i = 0; i < MAX; i++)   //由於數都是從數字末尾開始放 所以無關0要跳過
{
if (c[i] == 0 && flag == 1) continue;
else
{
flag = 2;
cout << c[i];
}
}
cout << endl;
}


void BigX(int m, int n)   //超大數乘法核心
{
for (int i = m - 1; i >= 0; i--)
{
int sum = (MAX-1) - (m - 1 - i);   //關鍵 具體參考乘法公式
for (int j = n - 1; j >= 0; j--)
{
int part1 = a[i] * b[j];
c[sum] += part1;
int part2 = c[sum];
c[sum] %= 10;
c[--sum] += part2 / 10;
}
}
output(m,n);
}

int main()
{
while (gets_s(ca),gets_s(cb))
{
/*初始化*/
memset(c, 0, sizeof(c));
memset(a, 0, sizeof(a));
memset(b, 0, sizeof(b));
////////////////////////
int m = strlen(ca);
int n = strlen(cb);
for (int i = 0; i < m; i++)a[i] = ca[i] - '0';  //類型轉化
for (int i = 0; i < n; i++)b[i] = cb[i] - '0';
BigX(m, n);
cout << endl;
}
return 0;
}