Question

I have the following code written in both C++ and C#

 int i=0;
 ++i = 11;

After this C# compiler brings an error

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

But C++ compiler generate this code with no error and I got a result 11 for value of i. What’s the reason of this difference?

Answer 1

The difference is that pre-increment operator is lvalue in C++, and isn’t in C#.
In C++ ++i returns a reference to the incremented variable. In C# ++i returns the incremented value of variable i.
So in this case ++i is lvalue in C++ and rvalue in C#.

From C++ specification about prefix increment operator

The type of the operand shall be an arithmetic type or a pointer to a
completely-defined object type. The value is the new value of the
operand; it is an lvalue.

P.S. postfix increment operator i++ isn’t lvalue in both C# and C++, so this lines of code will bring error in both languages.

 int i=0;
 i++ = 11;