One way (among many) you could handle this:
using Microsoft.VisualBasic;
public enum WeekDay
{
Monday, Tuesday, Wednesday, Thursday, Friday
}
public enum Week
{
One, Two, Three, Four
}
In a method:
int x = 0;
int y = 0;
int result;
string intCandidate = Interaction.InputBox("Please enter value for Day " + ((WeekDay)x).ToString() + " in Week " + ((Week)y).ToString());
if(Int32.TryParse(intCandidate, out result))
{
toys[x, y] = result;
}
else
{
throw new ArgumentException("You must input an integer.");
}
Consider whether you should also check the x,y variables to make sure they are in the proper range.
Why did I use Enums rather than just List<string>: just because I felt like doing it a slightly different way.
I wonder why you needed to use Visual Basic here; why not just use two NumericUpDown Controls in C# ?