Compiler Error CS0131

The left-hand side of an assignment must be a variable, property or indexer

In an assignment statement, the value of the right-hand side is assigned to the left-hand side. The left-hand side must be a variable, property, or indexer.

To fix this error, make sure that all operators are on the right-hand side and that the left-hand side is a variable, property, or indexer. For more information, see Statements, Expressions, and Operators (C# Programming Guide).

Example

The following sample generates CS0131.

// CS0131.cs
public class MyClass
{
    public int i = 0;
    public void MyMethod()
    {
        i++ = 1;   // CS0131
        // try the following line instead
        // i = 1;
    }
    public static void Main() { }
}

This error can also occur if you attempt to perform arithmetic operations on the left hand side of an assignment operator, as in the following example.

// CS0131b.cs
public class C
{
    public static int Main()
    {
        int a = 1, b = 2, c = 3;
        if (a + b = c) // CS0131
        // try this instead
        // if (a + b == c)
            return 0;
        return 1;
    }
}