[julia-users] How to Manipulate each character in of a string using a for loop in Julia ?

[Rishabh Raghunath]

Hello fellow Julia Users!!

How do you manipulate the individual characters comprising a string in 
Julia using a for loop ?
For example:
###################

a = "abcd"

  for i in length(a)
   a[i]+=1
 end

print(a)

####################
 I am expecting to get my EXPECTED OUTPUT as        "     bcde      "

 BUT I get the following error:  
##########################################

 ERROR: MethodError: `setindex!` has no method matching 
setindex!(::ASCIIString, ::Char, ::Int64)
 [inlined code] from ./none:2
 in anonymous at ./no file:4294967295

##########################################
I also tried using:

for i in eachindex(a) instead of the for loop in the above program .. And I 
get the same error..

Please tell me what i should do to get my desired output ..
Please respond ASAP..
Thanks..