在QB中RND函数并不是随机的，你可以在前面先输个randomize，以后每次输一个特殊值，就可以有不同的随机数了

5 randomize timer
另外，30行中的rnd建议不要(1)

CLS : RANDOMIZE TIMER
PRINT STRING$(14, "*") + "Guess Number" + STRING$(20, "*")
PRINT "*"; SPC(44); "*"
PRINT "*Please Input A Number" + STRING$(3, "-") + "0<A<100 || A=-1: END*"
PRINT "*"; SPC(44); "*"
PRINT STRING$(46, "*")
PRINT
b = INT(100 * RND)
DO
  INPUT "A=", A: IF A = -1 THEN EXIT DO
  IF A > b THEN
    PRINT "Big!"
  ELSEIF A < b THEN
    PRINT "Small!"
  ELSE
    PRINT "You Are Right!"
    EXIT DO
  END IF
LOOP
END

显示效果如下：
***************Guess Number*********************
*                                              *
* Please Input A Number---0<A<100 || A=-1: END *
*                                              *
************************************************

A=50
Small!
A=90
Big!
A=75
Small!
A=-1
Good Luck next time!

谢啦！

阿达,你没加RANDOMIZE TIMER.

10 RANDOMIZE TIMER
20 CLS
30 a = RND(1)
40 b = INT(100 * a)
50 DO
60 INPUT c
70 IF c = b THEN
80 PRINT "you are right!!!"
90 END
100 END IF
110 IF c > b THEN PRINT "big!!!"
120 IF c < b THEN PRINT "small!!!"
130 LOOP
140 END
我已经很克制了还有14行

随机换数字
10 RANDOMIZE TIMER
20 CLS
30 DO
40 a = RND(1)
50 b = INT(100 * a)
60 INPUT c
70 IF c = b THEN
80 PRINT "You are right!!!"
90 END
100 END IF
110 IF c > b THEN PRINT "Big!!!"
120 IF c < b THEN PRINT "Small!!!"
130 LOOP
140 END