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 Operators and expressions.

Example 1

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() { }  
}  

Example 2

The following sample generates CS0131 when assigning to a constant field.

// CS0131b.cs  
public class B  
{
    public static int Main()
    {
        const int j = 0;
        j = 1; // CS0131  
        // try the following lines instead
        // int j = 0; 
        // j = 1;
        return j;
    }  
} 

Example 3

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.

// CS0131c.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;  
    }  
}