大数乘法

void MUL(char str1[],char str2[],char result[])
{
	int len1 = strlen(str1),len2 = strlen(str2);
	int index = 0,carry = 0,temp = 0;;

	for (int i1 = len1 - 1; i1 >= 0; --i1)
	{
		index = len1 - 1 - i1;
		for (int i2 = len2 - 1; i2 >= 0; --i2)
		{
			temp = (result[index] - '0') + (str1[i1] - '0') * (str2[i2] - '0') + carry;

			result[index] = temp%10 + '0';
			carry = temp/10;

			++index;
		}

		if (carry > 0)
		{
			result[index] = (result[index] - '0') + carry + '0';
			carry = 0;
			++index;
		}
	}

	//去掉结果数字串中前面的0
	while (result[index] == '0' && index > 0)
	{
		--index;
	}

	result[++index] = '';

	int i =0,j = index - 1;
	while(i < j)
	{
		Swap(result[i],result[j]);
		++i;
		--j;
	}
}