Above sample modified.
Communication is not 'my' strong suit.
Naming schemes may be confusing.
naming scheme used in samples:
---credit_s = credit STRING (s)
---credit_n = credit var (n)
---creditf = credit function (f)
'your' choice (naming scheme)
original vars from first post in thread
Code:
string credit = 10000;  // <- can't set string value directly
// must use str functions (look in manual)
STRING credit[256];	// changed
var credits = 10000;  // to display on screen, this value should be copied to STRING credit 
// ...
// credits was modified?
// convert var to STRING
str_for_num(credit, credits); // converts / copies credits (var) to STRING credit

If credits (var) is modified, and the modification should be shown on screen, the (STRING) value of credits (var) should be copied to credit (STRING) via str_for_num.
creditf functions in samples were / are optional example convenience / inconvenience functions.
The functions just encapsulate the conversion (var to STRING) (+etc.).
STRINGs are modified / assigned values through str functions.
So:
Code:
string credit = 100;  // <- error!?