Here's a simple console application code, which returns a result I do not understand completely.
Try to think whether it outputs 0, 1 or 2 in console:
using System;
namespace ConsoleApplication
{
class Program
{
static void Main()
{
int i = 0;
i += Increment(ref i);
Console.WriteLine(i);
Console.ReadLine();
}
static private int Increment(ref int i)
{
return i++;
}
}
}
The answer is 0.
What I don't understand is why post increment i++
, from the Increment
method, which is executed on a ref
(not on a copy of the passed variable) does increment the variable, but it just gets ignored later.
What I mean is in this video:
Can somebody explain this example and why during debug I see that value is incremented to 1, but then it goes back to 0?
i += Increment(ref i);
is equivalent to
i = i + Increment(ref i);
The expression on the right hand side of the assignment is evaluated from left to right, so the next step is
i = 0 + Increment(ref i);
return i++
returns the current value of i
(which is 0), then increments i
i = 0 + 0;
Before the assignment the value of i
is 1 (incremented in the Increment
method), but the assignment makes it 0 again.
i think the "magic" here is just operation precedence the order of operations
i += Increment(ref i)
is the same as
i = i + Increment(ref i)
the + operation is executed left to right
so first we take i ... wich is 0 at that time ...
then we add the result of Increment(ref i) ... which is also 0 ... 0+0=0 ... but wait ... before we get that result i is actually incremented ...
that increment takes place after the left operand of our + operation has ben evaluated ... so it does not change a thing ... 0+0 still is 0 ... thus i is assigned 0 after the + operation has been executed
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