For those not familiar, ISO 8583 is a standard for credit card and ATM card transactions. ISO 8583 defines the message format used in these transactions.
The
Trx Framework implements ISO 8583 in C#.
jPOS implements ISO 8583 in Java.
perlPOS implements ISO 8583 in PERL, but the source is not yet ready for public release.
The work of all of these people could save you an
enormous amount of effort. Effectively, you will have a porting task instead of a design task.
Or, you could just use C# or Java and forget about C for awhile. :p