Sort three input numbers

I am looking at this assignment:

Write a program that takes three inputs and outputs them in ascending order.

I had used the following LMC simulator: https://www.101computing.net/LMC/#

And this is what I've done so far:

INP 901 Input num1
STA 318 Store num1 in address 18
INP 901 Input num2
STA 319 Store num2 in address 19
INP 901 Input num3
STA 320 Store num3 in address 20
SUB 219 Subtract num2 from num3
BRP 810 Jump to address 10 if it is zero or positive (J1)
LDA 519 Load num2 from address 19
STA 320 Store num3 in address 20
LDA 520 Load num3 from address 20 (J1)
SUB 218 Subtract num1 from num3
BRP 815 Jump to address 18 if it is zero or positive (J2)
LDA 518 Load num1 from address 18
STA 320 Store num3 in address 20
LDA 520 Load num3 from address 20 (J2)
OUT 902 Output result
HLT 000 Stop program
DAT     Data num1
DAT     Data num2
DAT     Data num3

I only achieved to find the largest number, but I do not know how to arrange them in ascending order.

How can I also output the other two values in their right order?

Solution

First some comments on the code you provided:

That code doesn't parse on the simulator you linked to. This is because you combine mnemonics (3-letter codes) with the instruction codes (3-digit numbers). You should just use the mnemonics. So for instance, write INP, not INP 901.
Use labels. So for instance, don't write STA 318, which by the previous point really should be STA 18, but write STA num1, and define that label at the corresponding DAT line: num1 DAT. Note that the simulator you linked to doesn't even accept a DAT without label.
Use a separating character (like # or ;) at the start of the comments. Although some simulators will not mind that you just write comments without such a separator, it is better practice to use it. Also the simulator you linked to does not seem to support comments.
When you comment, make comments that go beyond the mere description of the instruction. For instance, it is not useful to put Stop program as a comment next to HLT. That should be evident. Instead make comments that explain the higher purpose of an instruction in your algorithm. For instance "is num3 greater than num2?" would be good comment at the first BRP.

So applying the above changes to your code, you would get this:

#input: 3 2 1
         INP
         STA num1
         INP
         STA num2
         INP
         STA num3

comp23   LDA num3 # is num2 <= num3?
         SUB num2
         BRP sorted23 # yes

         LDA num2 # no: copy it to num3
         STA num3

sorted23 LDA num3 # is num1 <= num3?
         SUB num1
         BRP output # yes: we're done

         LDA num1 # no: copy it to num3
         STA num3

output   LDA num3 # output the greatest
         OUT
         HLT
num1     DAT
num2     DAT
num3     DAT

<script src="https://cdn.jsdelivr.net/gh/trincot/lmc@v0.815/lmc.js"></script>

This will print the greatest value among the inputs. Now to sort the input, you need to swap pairs of values. For swapping you could use a fourth variable (temp). For instance, to swap num2 with num3, you would write:

   LDA num3
   STA temp # temporary save num3 here
   LDA num2
   STA num3 # now both are the same value
   LDA temp # but we still have a copy...
   STA num2

You can sort 3 numbers with maximum three swaps. If there is a third swap involved, it will be the same kind of swap as the first swap.

Here is how that would work:

#input:3 2 1
          INP
          STA num1
          INP
          STA num2
          INP
          STA num3

comp23    LDA num3 # is num2 <= num3?
          SUB num2
          BRP sorted23 # yes

          LDA num3 # no: swap num2 and num3
          STA temp
          LDA num2
          STA num3
          LDA temp
          STA num2

sorted23  LDA num2 # is num1 <= num2
          SUB num1
          BRP sorted123 # yes: we're done

          LDA num2 # no: swap num1 and num2
          STA temp
          LDA num1
          STA num2
          LDA temp
          STA num1
          BRA comp23 # repeat once

sorted123 LDA num1 # output the sorted list
          OUT
          LDA num2
          OUT
          LDA num3
          OUT
          HLT
num1      DAT
num2      DAT
num3      DAT
temp      DAT # used for swapping

<script src="https://cdn.jsdelivr.net/gh/trincot/lmc@v0.815/lmc.js"></script>

In my opinion the simulator you pointed to is not the best. The one I use in this answer is available here -- I am its author.