New Zealand Bank Account Format Display - account

Question

I am to display New Zealand and Australian bank accounts in reports, formatted according to a custom format supplied by the user. For example, NZ bank accounts can be 00-0000-0000000-000 with the last digit (bank account suffix) being optional. There are two parts of the format:
Placement of dashes
2 digit prefix
Sample formatted bank accounts can be 01-1234-1234567-55 and 01-1234-1234567-002. The bank accounts are stored in the database without any formatting. When I tried String.Format("{0:00-0000-0000000-00#}",121234123456712) it does not return the expected 12-1234-1234567-12 but 01-2123-4123456-712.
Understandably I could always test the length of the bank account and do a switch statement, but the format is user defined.
The following ensures the dashes are placed correctly and the suffix is correct:
// ensure there is a format to use and a bank account is present
if (bankaccountformat != "" && bankaccountformat.Contains('-') && bankaccount != "")
{
int i = 0;
foreach (char dash in bankaccountformat)
{
// add dash in bank account, if bank account is long enough
if (dash == '-' && bankaccount.Length > i)
{
bankaccount = bankaccount.Insert(i, "-");
}
i++;
}
}
The issue is not if the account is valid or not, it is the formatting. Please let me know of a better way to format the account.

Answer 1

You do not mention which programming language you use. Anyhow, it seems you use an array. That can be tricky.
In BASH I would use string manipulation, like in this script (fmat):
#!/bin/bash
#only numbers allowed
[[ ! "$1" =~ ^[0-9]+$ ]] && echo "Error: enter numbers only" && exit
s=$1
l=${#s}
r=l-13
#minimal number of digits is 13, maximum 16
[[ r -lt 0 || r -gt 3 ]] && echo "Error: enter 13-16 digits" && exit
#first 13 digits
a=${s:0:2}"-"${s:2:4}"-"${s:6:7}
#when 14-16 digits
a=$a"-"${s:13:r}
echo $a
fmat 011234123456755 gives 01-1234-1234567-55
fmat 0112341234567002 gives 01-1234-1234567-002
fmat 0112341234567 gives 01-1234-1234567
If you use something else than BASH, then at least this gives some hints.