说明：   本程序需在DOS下运行。每运行一次可执行程序random.exe，即可显示任意两个 16进制数的加法或减法表达式及其运算结果。在减法运算中，如果被减数小于减数，显示 “Divide Overflow”的提示信息。
(the process required under the DOS operating. Every time running executable random.exe can display any number of two 16-band addition or subtraction of expression and the results of operations. The subtraction operation, if less than subtrahend minuend, shows that the "Divide Overflow" message.)