What does error CS1031 mean in C#?

CS1031 means the compiler expected a type name and found something else — a number, a value, or nothing. Typical cases: 'new 5()' instead of 'new Dog()', an empty generic 'List<>', or a cast with no type. Fix: put an actual type name where the message points.

How is CS1031 different from CS0246?

CS1031 means the grammar slot needs a type but got a non-type token. CS0246 means a type name was there but the compiler could not find that type — usually a typo or missing using. First fix the shape, then the spelling.

Compiler error · error CS1031

Type expected

A grammar slot only accepts a type name — int, string, List<int>, Dog. It got a value instead. This is the type-shaped sibling of CS1001.

See it happen

var item = new 5();   // 'new' needs a type, and 5 is a value

Where types are required

Slot	Broken	Fixed
after `new`	`new 5()`	`new Dog()`
declaration	`5 count = 0;`	`int count = 0;`
generic argument	`new List<>()`	`new List<int>()`
cast	`(int) x` △ vs `()x`	`(int)x`
parameter	`void F(5)`	`void F(int n)`

Cause 1: a value where a type goes

var price = new 9.99();   // you probably meant a class

double price = 9.99;      // you had the value already — no new needed
Console.WriteLine(price);

This is the most common version: `new` is for creating objects. A double is a value you just write.

Cause 2: an empty generic argument list

var items = new List<>();

var items = new List<string>();
Console.WriteLine(items.Count);

Cause 3: a parameter with no type

void Show(5)     // a parameter needs a type AND a name — this has a value
{
}

void Show(int value)   // type, then name
{
    Console.WriteLine(value);
}
Show(0);

Cause 4: a typo made the type disappear

If you meant a type but the error says "type expected", check whether the name morphed into punctuation — an accidental . or a deleted word. Then check separately whether the type exists: that second problem is CS0246.

Error	Meaning
CS1031	There is no type token in the slot at all
CS0246	A type name is there, but unknown (typo / missing using)

Frequently asked

What does CS1031 mean?

The compiler expected a type name and found a value or nothing. Put an actual type in the flagged slot — after new, in a declaration, or inside a generic's angle brackets.

CS1031 vs CS0246?

CS1031: wrong shape — no type where one is required. CS0246: right shape but unknown type. Fix the shape first, then the spelling.

Checklist

Look at the slot the error points to: new, declaration, generic, or cast.
Is there a value where a type belongs? Replace it with the type.
Angle brackets empty? Fill in the type argument.
Declaration with no type and no var? Add one.
Type name looks right but still fails? That's CS0246 — check spelling and usings.