CODEWITHSUNDEEP
c#.net
Elena
Elena

Reputation: 839

question about the usage of var keyword

I want to have something like:

var somevar;
if (cond)
{
  var= something;
  // a lot of code
}
else var = somethingElse;

However the compiler screams that a var should be initialized before using it in this way. How to do it. or how to accomplish this situation?

Upvotes: 4

Views: 300

Answers (10)

Ikaso
Ikaso

Reputation: 2268

You use the keyword var as a variable. replace var with somevar in the example.

Upvotes: 1

andrewjsaid
andrewjsaid

Reputation: 489

If 'something' and 'somethingElse' are of the same type, initialize somevar to the default of that type.

var somevar = default(TYPE GOES HERE);
if (cond)
{
  somevar = something;
  // a lot of code
}
else somevar = somethingElse;

Upvotes: 0

nik0lai
nik0lai

Reputation: 2655

You can use the object keyword but you still need to know what type it is when unboxing it so the var is a better idea if assigned to when declaring as said previously.

object a = something;
SomeCustomObject b = (SomeCustomObject)a;

Upvotes: 0

Justin Niessner
Justin Niessner

Reputation: 245429

You can't. When using var, you have to initialize the variable in the declaration...otherwise there is no way the compiler knows what type to make it.

Variables defined using var are still statically typed...the compiler just infers the type based on the assignment in the declaration. If you're looking for something that is dynamically typed, you could try the dynamic type if you're using .NET 4.0.

In your case, you need to specify the type at declaration.

Upvotes: 8

Larry Hipp
Larry Hipp

Reputation: 6255

The article below gives great detail into how var can be used.

The var keyword instructs the compiler to infer the type of the variable from the expression on the right side of the initialization statement. The inferred type may be a built-in type, an anonymous type, a user-defined type, or a type defined in the .NET Framework class library.

var can only be used when a local variable is declared and initialized in the same statement; the variable cannot be initialized to null, or to a method group or an anonymous function.

Implicitly Typed Local Variables (C# Programming Guide)

Upvotes: 0

CodingGorilla
CodingGorilla

Reputation: 19842

As other's have mentioned, var is still a static type, it just means that the compiler infers that type at compile time, not runtime.

I think this is what you want:

object somevar;
if (cond)
{
  somevar = something;
  // a lot of code
}
else somevar = somethingElse;

Upvotes: 3

Adam Houldsworth
Adam Houldsworth

Reputation: 64487

If both values of the condition are the same type, say string, do something like this:

var somevar = "";

To initialise it.

Upvotes: 2

GvS
GvS

Reputation: 52518

When declaring a variable using var, you must immediatly assign a value to it, so the compiler can know its type.

Although you could make a compiler that is smart enough to find the first usage, the C# compiler does not understand this code.

You could use:

var someVar = cond ? someThing : someThingElse;
if (cond) {
   // A lot of code
}

If someThing and someThingElse are of the same type. I think this is clearer to understand the possible values of someVar, but you test for cond twice.

Upvotes: 1

BFree
BFree

Reputation: 103740

Don't use var in that situation. The way the compiler figures out what type your variable is, is by analyzing what's on the right hand side. If you're not giving it anything on the right side, there's no way for the compiler to figure it out.

Upvotes: 1

Hans Kesting
Hans Kesting

Reputation: 39284

"var" is just a means to instruct the compiler to derive the exact type. But for that to work, you need to initialize it with an expression that returns that type.

Or don't use var but use the type you know that both expression will assign later.

Upvotes: 2

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