你找找，本吧有一个帖子转论述各种各样的形状输出。
你这个菱形，我记得，最好的方案是用绝对值函数。

Dim n, i, j
n = 6
For i = 1 To n
For j = i To n - 1
Print ; " ";
Next
For j = 1 To i * 2 - 1
Print ; "*";
Next
Print
Next
For i = n - 1 To 1 Step -1
For j = i To n - 1
Print ; " ";
Next
For j = 1 To i * 2 - 1
Print ; "*";
Next
Print
Next

根据2楼的建议，使用绝对值函数，写个更简单的代码：
for i=-4 to 4
?tab(5-abs(i));
for j=abs(i)-4 to 4-abs(i)
?"*";
next j
?
next i