VB.NET vs C# integer division

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
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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.

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VB.NET integer division operator is \, not /.

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"Division is performed differently in C# and VB. C#, like other C-based languages truncates the division result when both operands are integer literals or integer variables (or integer constants). In VB, you must use the integer division operator (\) to get a similar result."

Source

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最佳答案

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

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In C#, integer division is applied with / when both numerator and denomenator are integers. Whereas, in VB.Net '/' results in floating point divsion, so for integer division in VB.Net use \. Have a look at this MSDN post.


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