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