怎么调试这个VB语言呢?

dim  a(i),n as intenger
      for i = 0 to 19
         if a(i)>0 then 
            n1=n1+1
           else 
              if a(i)=0 then
                 n2=n2+1
              else 
                  n3=n3+1
              end if
         end if
     next
print “正数个数="n1
       “0的个数="n2
       “负数个数="n3