大整数加减，加法很容易，减法的功能为输入两个大整数相减，考虑到了小数减大数结果前加符号，然后进位等功能。-Large integer addition and subtraction, addition is easy, subtraction functions as an input two large integers subtraction, taking into account the plus sign in front of large numbers of decimal subtraction results, and then carry other functions.