Calling 32-bit NAG C DLL functions from Visual Basic

4stopit = 0rk = 3rk = 1where FALSE = 0 and TRUE = 1. The above example illustrates that, by default, enumeratorsin a givenCenumeration type declaration start at zero and increase by 1 as thedeclaration is read from left to right. However, if a given enumerator is assigned a valuethen subsequent enumerators continue the progression from the assigned value.StructuresMany of the DLL routines use structures in their argument lists. Sometimes, for examplein the d02 and e04 chapters, these structures are rather complicated and may contain otherstructures. When the structure is relatively simple it is often convenient to dene a VisualBasic user-dened type and then make a direct call to the DLL routine. Complicatedstructures are most easily dealt with by the use of an auxiliary DLL (this is illustrated inthe Optimize example in Appendix C).A structure that is required by nearly all of the routines is the type NagError. This isdened as:typedef struct fint codeBoolean printchar message[512]void (*handler)(char*, int*,char*)Integer errnumg NagErrorThe corresponding Visual Basic user-dened type is:Type NagErrorTypecode As Longprintm As LongMessage(511) As String * 1handler As Longerrnum As LongEnd Typewhere both int, Integer and Boolean types have been replaced by Long and the pointerto the handler function has been replaced by a structure memberoftype Long.As another example the type Nag Spline (used by routines e02bac and e02bbc) is denedas:typedef struct fInteger ndouble *lamdadouble *cInteger init1Integer init2g Nag Spline