VB.NET vs C# integer division [duplicate]

Question

Anyone care to explain why these two pieces of code exhibit different results?

VB.NET v4.0

Dim p As Integer = 16 Dim i As Integer = 10 Dim y As Integer = p / i //Result: 2 

C# v4.0

int p = 16; int i = 10; int y = p / i; //Result: 1 

Answer 1

When you look at the IL-code that those two snippets produce, you'll realize that VB.NET first converts the integer values to doubles, applies the division and then rounds the result before it's converted back to int32 and stored in y.

C# does none of that.

VB.NET IL Code:

IL_0000:  ldc.i4.s    10  IL_0002:  stloc.1      IL_0003:  ldc.i4.s    0A  IL_0005:  stloc.0      IL_0006:  ldloc.1      IL_0007:  conv.r8      IL_0008:  ldloc.0      IL_0009:  conv.r8      IL_000A:  div          IL_000B:  call        System.Math.Round IL_0010:  conv.ovf.i4  IL_0011:  stloc.2      IL_0012:  ldloc.2      IL_0013:  call        System.Console.WriteLine 

C# IL Code:

IL_0000:  ldc.i4.s    10  IL_0002:  stloc.0      IL_0003:  ldc.i4.s    0A  IL_0005:  stloc.1      IL_0006:  ldloc.0      IL_0007:  ldloc.1      IL_0008:  div          IL_0009:  stloc.2      IL_000A:  ldloc.2      IL_000B:  call        System.Console.WriteLine 

The "proper" integer division in VB needs a backwards slash: p \ i

Answer 2

In VB, to do integer division, reverse the slash:

Dim y As Integer = p \ i 

otherwise it is expanded to floating-point for the division, then forced back to an int after rounding when assigned to y.