同时声明和分配多个字符串变量

You can to do it this way:

string Camnr = "", Klantnr = "", ... // or String.Empty

Or you could declare them all first and then in the next line use your way.

You can do it like:

string Camnr, Klantnr, Ordernr, Bonnr, Volgnr;// and so on.
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = string.Empty;

First you have to define the variables and then you can use them.

Try with:

 string Camnr, Klantnr, Ordernr, Bonnr, Volgnr, Omschrijving;
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = string.Empty;

Try

string     Camnr , Klantnr , Ordernr , Bonnr , Volgnr , Omschrijving , Startdatum ,    Bonprioriteit , Matsoort , Dikte , Draaibaarheid , Draaiomschrijving , Orderleverdatum , Regeltaakkode , Gebruiksvoorkeur , Regelcamprog , Regeltijd , Orderrelease ;

and then

Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = Startdatum = Bonprioriteit = Matsoort = Dikte = Draaibaarheid = Draaiomschrijving = Orderleverdatum = Regeltaakkode = Gebruiksvoorkeur = Regelcamprog = Regeltijd = Orderrelease = "";

string Camnr , Klantnr , Ordernr , Bonnr , Volgnr , Omschrijving , Startdatum , Bonprioriteit , Matsoort , Dikte , Draaibaarheid , Draaiomschrijving , Orderleverdatum , Regeltaakkode , Gebruiksvoorkeur , Regelcamprog , Regeltijd , Orderrelease;
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = Startdatum = Bonprioriteit = Matsoort = Dikte = Draaibaarheid = Draaiomschrijving = Orderleverdatum = Regeltaakkode = Gebruiksvoorkeur = Regelcamprog = Regeltijd = Orderrelease = string.Empty;

An example of what I call Concatenated-declarations:

string Camnr = "",
Klantnr = "",
Ordernr = "",
Bonnr = "",
Volgnr = "",
Omschrijving = "",
Startdatum = "",
Bonprioriteit = "",
Matsoort = "",
Dikte = "",
Draaibaarheid = "",
Draaiomschrijving = "",
Orderleverdatum = "",
Regeltaakkode = "",
Gebruiksvoorkeur = "",
Regelcamprog = "",
Regeltijd = "",
Orderrelease = "";

Just my 2 cents, hope it helps someone somewhere.

Fairly old question but incase someone goes back.
This isn't as compact as the other answers above, but fairly readable and easier to type using Visual Studio Multi-Line selection shortcut [Alt+ Shift + ↑] (or other directions)

string Camnr = string.Empty;
string Klantnr = string.Empty;

Type out all variable names on new lines. Multi-Select in front of them an type "string". Multi-Select behind them and type "= string.Empty;".

Just a reminder: Implicit type var in multiple declaration is not allowed. There might be the following compilation errors.

var Foo = 0, Bar = 0;

Implicitly-typed variables cannot have multiple declarators

Similarly,

var Foo, Bar;

Implicitly-typed variables must be initialized

string a = "", b = a , c = a, d = a, e = a, f =a;

^{All the information is in the existing answers, but I personally wished for a concise summary, so here's an attempt at it; the commands use int variables for brevity, but they apply analogously to any type, including string.}

To declare multiple variables and:

• either: initialize them with separate values:

int i = 0, j = 1; // declare and initialize each, single-type only.
// Note: `var` is NOT supported as of C# 8.0, but see below.


// ===
// C#  7.0+ / .NET Framework 4.7+ using syntactic sugar based on *value tuples*:


// Infer the types from the RHS tuple elements.
var (i, s) = (0, "hi");


// Explicitly type the individual variables.
(int i, string s) = (0, "hi");

• or: initialize them all with the same value:

int i, j;    // *declare* first (`var` is NOT supported)
i = j = 42;  // then *initialize*


// Single-statement alternative that is perhaps visually less obvious:
// Initialize the first variable with the desired value, then use
// the first variable to initialize the remaining ones.
int i = 42, j = i, k = i;

What doesn't work:

• Unless you use the value-tuple syntax, you cannot use var in the above statements, because var only works with (a) a declaration that has an initialization value (from which the type can be inferred), and (b), as of C# 8.0, if that declaration is the only one in the statement (otherwise you'll get compilation error error CS0819: Implicitly-typed variables cannot have multiple declarators).

• Placing an initialization value only after the last variable in a multiple-declarations statement initializes the last variable only:

  int i, j = 1; // initializes *only* j

One can declare and initialize multiple variables in the following way nowadays:

var (anInt, aFloat, aBoolean, aChar, aString, anArray, aRecordType, anObjectType) =
(1, 2.14, true, 'a', "C# is awesome!", new[] { "Asia", "Europe" } , new Country { Name = "India"}, new City { Name = "Kolkata"} );
Console.WriteLine(anInt);
Console.WriteLine(aFloat);
Console.WriteLine(aBoolean);
Console.WriteLine(aChar);
Console.WriteLine(aString);
Array.ForEach(anArray, Console.WriteLine);
Console.WriteLine(aRecordType.Name);
Console.WriteLine(anObjectType.Name);

Following are the definition of required custom types:

internal record Country { internal string Name {get; set;}}
internal class City { internal string Name {get; set;}}

This has been tested on .NET 5/C# 9.