Decreasing value of minimum int results in maximum int

I'm currently reading through C# 4.0 In A Nutshell, and in chapter 2 it states that if an int object has a value of int.MinValue (-2147483648) and the value is decreased, as the value cannot go any lower, it goes to the highest value, int.MaxValue (2147483647):

int a = int.MinValue;
Console.WriteLine(a); //-2147483648
a = a-1;
Console.WriteLine(a); //-2147483648
Console.WriteLine (a == int.MaxValue);  // True

The book then goes on to mention how you can protect from this happening using checked.

However, I'm wondering why this is possible? Surely this could cause a lot of issues if its not protected with checked?

Is it not a bit of a flaw in the design? Why would anyone want a minimum value to become a maximum value?

Furthermore, I've noticed VB.NET will throw an 'Arithmetic overflow' instead of letting this happen:

Dim a As Integer
开发者_StackOverflow社区a = Integer.MaxValue
a = a + 1
Response.Write(a) 'Arithmetic overflow exception here

Sometimes it is desired behaviour. Other times, it simply isn't necessary to deal with and check for overflows, as they slow down program execution. Take a game drawing unbound (FPS). At 1000FPS, a small 1ms extra check could have a significant affect on framerate. Other times, it may be expected execution (I've only seen one use of this to date) - it flows on from what happens in C#'s ancestor - C++ and C.

Also, please note that the default behaviour (checked or unchecked) varies between configurations and environments:

If neither checked nor unchecked is used, a constant expression uses the default overflow checking at compile time, which is checked. Otherwise, if the expression is non-constant, the run-time overflow checking depends on other factors such as compiler options and environment configuration.

Since the code you posted is non-constant (and also due to various environment variables), no checking for overflows is performed.

It is a matter of language design - why this happens has to do with the binary representation of numbers. In .NET this is done with two's complement, hence the overflow issue.

The designers of VB.NET have decided to not allow such overflow/underflow issues.

The designers of C# have decided to leave control to the programmer.

It is possible that your programm automatically check overflow: right click on project file, select Build, than select Advanced button in right bottom corner. In the opened window check Check Arithmetical Overflow checkbutton.