Programming :: Represent Alphabet Into A Array?

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' "'$char" like this would not work.