高精度大整数乘法,对于大整数比较方便的输入方法是，按字符型处理，两个成熟存储在字符串数组s1，s2中，计算结果存储在整型数组a中。-Precision large integer multiplication, more convenient for large integer input method is handled by the character, two mature stored in an array of strings s1, s2, the calculation res