大数乘法

void mul(char a[],char b[])
{
/****************装换****************/
	int num1[LEN];
	int num2[LEN];
	for (int i = 0; i < LEN; i++){
		num1[i] = 0;
		num2[i] = 0;
	}
	int lena = strlen(a);
	int lenb = strlen(b);

	for (int i = lena - 1,j = 0; i >= 0; i--){
		num1[j++] = a[i] - '0';
	}

	for (int i = lenb - 1,j = 0; i >= 0; i--){
		num2[j++] = b[i] - '0';
	}
/************************乘积*************/	
	int sum[LEN];
	for (int i = 0; i < LEN; i++){
		sum[i] = 0;
	}

	for (int i = 0; i < lena; i++)
		for (int j = 0; j < lenb; j++){
			sum[i + j] += num1[i] * num2[j];
			if (sum[i + j] >= 10){
				sum[i + j + 1] += sum[i + j] / 10;
				sum[i + j] %= 10;
			}
		}
	/*******************打印*******************/
	int i;
	for (i = LEN - 1; i > 0; i--){
		if (sum[i] != 0)
			break;
	}
	for (; i >= 0; i--)
		cout << sum[i];
	cout << endl;
}