Incrementation not showing in MessageBox and variable values being changed

Question

I have two questions about this code...

1. Why is that at line 10 it starts keeping the current value. For example,

   int a = 7
   

   (a += 4) Which is 11 is brought over to the next line of code (a -= 4) now making it 7. Instead of just using it initial declaration for the variable a which is 7. How come I don't get 3 ? Is the = in the += operator changing what I initially declared it in the beginning of the code ? Does a still hold the value 7 in memory, or does those statements change that?

2. At the last MessageBox.Show() statement. I increment a by 1 using a++. However, I get the same value I had for the previous MessageBox.Show(). How come it didn't increment ??

This is the code:

private void button1_Click(object sender, EventArgs e)
{
    int a = 7;
    int b = 3;

    MessageBox.Show((a + b).ToString(), "a+b");
    MessageBox.Show((a - b).ToString(), "a-b");
    MessageBox.Show((a * b).ToString(), "a*b");
    MessageBox.Show((a / b).ToString(), "a/b");
    MessageBox.Show((a += 4).ToString(), "a+=4"); //adds 4 to a
    MessageBox.Show((a -= 4).ToString(), "a-=4"); //substracts 4 from a
    MessageBox.Show((a *= 4).ToString(), "a*=4"); //multiplies 4 from a
    MessageBox.Show(a++.ToString(), "a++"); //adds 1 to a
}

Answer 1

How come I don't get 3 ? Is the "=" in the "+=" operator changing what I initially declared it in the beginning of the code ?

The += operator is equivalent to:

a = a + 4

Effectively assigning a new value to a.

Does "a" still hold the value 7 in memory, or does those statements change that?

It doesn't. After your first assignment, it changes.

At the last MessageBox.Show() statement. I increment "a" by 1 using "a++". However, I get the same value I had for the previous MessageBox.Show(). How come it didn't increment ??

That's what happens when you use ++ as a postfix. The docs say:

The second form is a postfix increment operation. The result of the operation is the value of the operand before it has been incremented.

But, if you use it as a prefix:

MessageBox.Show((++a).ToString(), "++a");

You'll see the updated value, again as the docs say:

The first form is a prefix increment operation. The result of the operation is the value of the operand after it has been incremented.