自己苦思冥想多时，不得其解！望各位赐教！

问题是这样的：

随机产生0-20个数，建立一个有6个数据的等差数列，count用来记录试验次数。一旦形成等差数列，则打印输出，同时结束程序运行

private sub command1_click()
count n =6
dim a%(n),i%,count&,d%
randomize timer
do while true
for i = 1 to n
a(i)=rnd*20
next i
count = count +1
d=a(2)-a(1)
for i = 1 to n
if a(i)-a(i-1) <> d then exit for
next i
if ______________________________ then
for i = 1 to n
?a(i);
?count
_________________
end if
loop
end sub

题中划线的地方，却想不出正解

感谢，我运行了一下，

我觉得变量B可以省略
private sub command1_click()
const n =6
dim a%(n),i%,count&,d%
randomize timer
do while true
for i = 1 to n
a(i)=rnd*20
next i
count = count +1
d=a(2)-a(1)
for i = 1 to n
if a(i)-a(i-1) <> d then exit for
next i
if i=n+1 then
for i = 1 to n
?a(i);
?count
next i
end if
loop
end sub

如此运行，程序相应好慢，不知为何？