Adding number to integer variable with value already as int.MaxValue

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Surprisingly, the first line throws mentioned error. But the for loop works. For loop executed too and performs addition as well. It seems as if we are moving in circles while dealing with integers. Any insight on why this happens?

C#

// int i = int.MaxValue + 100; // Error: The operation overflows at compile time in checked mode
// Following works
for (int i = int.MaxValue; i > 0; i++)
{
  i = i + 10;

  Console.WriteLine(i);
}

Posted 22-Aug-11 22:42pm

dan!sh

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4 solutions

Solution 1

What do you mean with 'works'? It silently overflows, that's all.

Posted 22-Aug-11 22:47pm

CPallini

Comments

dan!sh 23-Aug-11 5:42am

And that's weird. We, a developer, may miss out on this kind of thing which can result in huge problems.

CPallini 23-Aug-11 5:48am

well, we're developers, not spoon-fed children.

dan!sh 23-Aug-11 6:05am

Not everyone is. :)

Solution 2

MaxValue +1 == Maxvalue *-1;

So when it is at the top it will return to the maximum negative value in the Int range

Posted 22-Aug-11 22:48pm

Herman<T>.Instance

Solution 4

Just put i-- and it will overflow. :)

Posted 22-Aug-11 22:51pm

Prerak Patel

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OriginalGriff · Accepted Answer · 2011-08-22T22:48:00

Because integers do indeed move in circles! If you exceed the MaxValue, then you get into negative territory. Anything with the top bit set in a signed integer is a negative number, and the Max value is a single 0 bit in an otherwise 1 filled 32 bit word. If you add a value to that, then the new value will have the top bit set, and thus be negative.
It's a little annoying that it doesn't throw an overflow exception, but that's life!

The other line complains at compile time because it rightly spots that if you add a number to it's maximum value, it will overflow.