Question: I would like to have it round up to 100 using stringformat, not math.round because the way in the code I can't use math.round.

Answer: 
If you set your precision to a single digit like this, the number will be rounded up to 100.0. You can use string interpolation and not have to specify String.Format like this:

```
Console.WriteLine($"{99.99:0.0}");

```
If you want to round the number to the nearest integer, you can try:

```
var str = string.Format("{0:.}", 99.99); // Will return "100"

```

If you want to always have one digit after the delimiter, you can change it to:

```
var str = string.Format("{0:.0}", 99.99); // Will return "100.0"

```

You can always check the official documentation for the entire set of options:
[String.Format Method](https://learn.microsoft.com/en-us/dotnet/api/system.string.format?view=net-5.0)