bash arrays

[ionguang]

i am trying to represent alphabet into a array, and then i can count the frequency
for example
array[a]=0
array[b]=0

but i find the index of the array seems to be
array[1]=0
array[2]=0

I was try this way get the ascii for them, actually I have done this in java and it is simple.
something like this format
array[ascii{a}-ascii{a}]=0
array[ascii{b}-ascii{a}]=0
I have done a lot of searching , but cannot get what I want.
'%d\n' "'$char" like this would not work.

[ionguang]

for i in {a..z}
do
alphabet[$i]=0
done

actually I try to do this at the beginning.

[ionguang]

Up up up
go HOLLAND