# Calculator: multiple variable coding question

**URL:** <https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422>\
**Category:** General\
**Created:** [15 February 2022 21:15 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422 "2022-02-15T21:15:22Z")\
**Posts on this page:** 15\
**Page:** 1

<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [15 February 2022 21:15 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/1 "2022-02-15T21:15:22Z")

</div>

Could someone help me to explain how one could write a (function node) code with multiple variables that are entered from a text field in the UI?

I would like to make a dilution calculator for my student (I am a chemist).  
The main formula is as follows:  
C1 \* V1 = C2 \* V2

The variables could be written down as followed:  
C1=((C2\*V2) / (V1))

V1=((C2\*V2) / (C1))

C2=((C1\*V1) / (V2))

V2=((C1\*V1) / (C2))

All the variables should be known except the one before the equal mark.  
example:  
V2=((C1\*V1)/(C2))

(Background info for fun)  
I took a volume of 1 litre (V1) that contains a concentration of 100 grams per litre (C1)  
I would like to end with a concentration of 25 grams per litre (C2). What is the final volume after dilution? (V2)

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<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [15 February 2022 21:44 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/2 "2022-02-15T21:44:48Z")

</div>

I am not sure exactly what you are asking, but possibly what you are looking for is the ui\_form node, which allows you have multiple fields in which the numbers could be entered, and all get passed to the next node when the Submit button is hit.

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<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [15 February 2022 21:50 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/3 "2022-02-15T21:50:35Z")

</div>

I re-read my question and made a little edit. It was a bit vague, sorry.  
My problem: I don't know how to write the code that should solve the equations.

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<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [15 February 2022 22:04 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/4 "2022-02-15T22:04:13Z")

</div>

May be something like this, leave the field you want answered empty

```auto
[{"id":"502b7419641df689","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"V1\":100,\"C1\":100,\"C2\":25,\"V2\":null}","payloadType":"json","x":130,"y":140,"wires":[["62f0b8d9.0608c"]]},{"id":"62f0b8d9.0608c","type":"ui_form","z":"bf9e1e33.030598","name":"","label":"","group":"2d4fe667.28f8ba","order":22,"width":0,"height":0,"options":[{"label":"S Volume","value":"V1","type":"number","required":false,"rows":null},{"label":"S Concentration","value":"C1","type":"number","required":false,"rows":null},{"label":"F Concentration","value":"C2","type":"number","required":false,"rows":null},{"label":"F Volume","value":"V2","type":"number","required":false,"rows":null}],"formValue":{"V1":"","C1":"","C2":"","V2":""},"payload":"","submit":"submit","cancel":"Reset","topic":"topic","topicType":"msg","splitLayout":"","className":"","x":220,"y":100,"wires":[["a0537cfa.753e3"]]},{"id":"a0537cfa.753e3","type":"function","z":"bf9e1e33.030598","name":"","func":"const formula = Object.keys(msg.payload).filter(e => !msg.payload[e]) \nif(formula.length === 1){\nswitch(formula[0]) {\n case \"C1\":\n msg.payload.C1 = ((msg.payload.C2*msg.payload.V2) / (msg.payload.V1));\n break;\n case \"V1\":\n msg.payload.V1 = ((msg.payload.C2*msg.payload.V2) / (msg.payload.C1));\n break;\n case \"C2\":\n msg.payload.C2 = ((msg.payload.C1*msg.payload.V1) / (msg.payload.V2));\n break;\n case \"V2\":\n msg.payload.V2 = ((msg.payload.C1*msg.payload.V1) / (msg.payload.C2));\n break;\n default:\n msg.payload.C1 = \"Error\";\n }\n}\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":340,"y":140,"wires":[["8ad333f6.78443","62f0b8d9.0608c"]]},{"id":"8ad333f6.78443","type":"debug","z":"bf9e1e33.030598","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":560,"y":140,"wires":[]},{"id":"2d4fe667.28f8ba","type":"ui_group","name":"demo","tab":"1caa8458.b17814","order":1,"disp":true,"width":"12","collapse":false},{"id":"1caa8458.b17814","type":"ui_tab","name":"Demo","icon":"dashboard","order":1,"disabled":false,"hidden":false}]

```

the function looks for the payload property key that is null.  
[edit] added a check for atleast 3 values.

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<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [15 February 2022 22:29 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/5 "2022-02-15T22:29:05Z")

</div>

I think there are only two different cases: where the final volume is unknown and where the final concentration is unknown.

So a function node to do the calculation might be like this

```auto
var result;

if (msg.hasOwnProperty('FinalConc')) {
    result = msg.InitialConc * msg.InitialVol / msg.FinalConc;
}
else if (msg.hasOwnProperty('FinalVol')) {
    result = msg.InitialConc * msg.InitialVol / msg.FinalVol;
}
msg.payload = result;
return msg;

```

If you suggest that the calculator needs to handle a question like "I diluted a solution from 1litre to 1.6litre. It's was then 0.7 Molar. What was the original concentration", it can:  
InitialVol = 1.6, InitialConc = 0.7, FInalVol = 1

You should of course check that all values are numeric and the denominator is not zero.

---

<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [16 February 2022 10:26 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/6 "2022-02-16T10:26:59Z")

</div>

This is brilliant! Thanks!

Now a method to not-change-the-results once the submit button is pressed 🤔 (the answer field i mean)

I am thinking of making 3 or 4 squares with infill fields.. each for another form of the equation.

C1=((C2\*V2) / (V1))

V1=((C2\*V2) / (C1))

C2=((C1\*V1) / (V2))

V2=((C1\*V1) / (C2))

Maybe then I can get the number to be unchangeable? or am I thinking wrong

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<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [16 February 2022 10:34 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/7 "2022-02-16T10:34:18Z")

</div>

Not sure what you mean, once you press submit and the answer is given, even if you press submit again the fields keep their values.

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<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [16 February 2022 10:35 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/8 "2022-02-16T10:35:53Z")

</div>

I can manually type something different in the answer field after pressing submit!

i will describe what I did to explain what I mean =D

step 1 fill in and leave 1 blank  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/3/d/3de9ed636ed2e09ec25d65bd51e99759b3b1fa98.png)

Step 2, pressed submit (and your wonderfull calc works! i am so happy)  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/5/4/54dab8a1c5f623e5afb581fe18944839ad294baf.png)

Step 3 "be an annoying student of the teacher and change numbers"  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/4/2/42a03c0e9c91c2000146140201d83648672e2ba5.png)

Step 4.... Students will use this to get away with stuff hahaha i know how inventive they are

Pressing submit after step 3 will not change anything so a fool could assume it to be correct =D

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<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [16 February 2022 10:45 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/9 "2022-02-16T10:45:20Z")

</div>

Ok I see. Store the values when the calc has been completed then the values will return if submitted again. Then later flow you can then retrieve them  
eg.

```auto
[{"id":"502b7419641df689","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"V1\":100,\"C1\":100,\"C2\":25,\"V2\":null}","payloadType":"json","x":130,"y":140,"wires":[["62f0b8d9.0608c"]]},{"id":"62f0b8d9.0608c","type":"ui_form","z":"bf9e1e33.030598","name":"","label":"","group":"2d4fe667.28f8ba","order":22,"width":0,"height":0,"options":[{"label":"S Volume","value":"V1","type":"number","required":false,"rows":null},{"label":"S Concentration","value":"C1","type":"number","required":false,"rows":null},{"label":"F Concentration","value":"C2","type":"number","required":false,"rows":null},{"label":"F Volume","value":"V2","type":"number","required":false,"rows":null}],"formValue":{"V1":"","C1":"","C2":"","V2":""},"payload":"","submit":"submit","cancel":"Reset","topic":"topic","topicType":"msg","splitLayout":"","className":"","x":220,"y":100,"wires":[["a0537cfa.753e3"]]},{"id":"a0537cfa.753e3","type":"function","z":"bf9e1e33.030598","name":"","func":"const formula = Object.keys(msg.payload).filter(e => !msg.payload[e]) \nif(formula.length === 1){\nswitch(formula[0]) {\n case \"C1\":\n msg.payload.C1 = ((msg.payload.C2*msg.payload.V2) / (msg.payload.V1));\n break;\n case \"V1\":\n msg.payload.V1 = ((msg.payload.C2*msg.payload.V2) / (msg.payload.C1));\n break;\n case \"C2\":\n msg.payload.C2 = ((msg.payload.C1*msg.payload.V1) / (msg.payload.V2));\n break;\n case \"V2\":\n msg.payload.V2 = ((msg.payload.C1*msg.payload.V1) / (msg.payload.C2));\n break;\n default:\n msg.payload.C1 = \"Error\";\n }\ncontext.set(\"value_store\", msg.payload)\nmsg.values = msg.payload;\n}else{\n msg.payload = context.get(\"value_store\");\n}\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":340,"y":140,"wires":[["8ad333f6.78443","62f0b8d9.0608c"]]},{"id":"8ad333f6.78443","type":"debug","z":"bf9e1e33.030598","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":520,"y":140,"wires":[]},{"id":"2d4fe667.28f8ba","type":"ui_group","name":"demo","tab":"1caa8458.b17814","order":1,"disp":true,"width":"12","collapse":false},{"id":"1caa8458.b17814","type":"ui_tab","name":"Demo","icon":"dashboard","order":1,"disabled":false,"hidden":false}]

```

msg.values now holds the inputted values for further processing.

---

<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [16 February 2022 10:48 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/10 "2022-02-16T10:48:33Z")

</div>

How are you so quick with this?  
Marvelous!

---

<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [16 February 2022 10:49 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/11 "2022-02-16T10:49:37Z")

</div>

Have you ever watched Rainman (joke, i function extremely well) If you have an inventive student, challenge them with harder tasks.

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<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [16 February 2022 10:54 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/12 "2022-02-16T10:54:24Z")

</div>

Hahahaha yes, I do and I understand the reference 😃

speaking of references....

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/3/d/3d87abaa84af2e7027f755c5bdadea7259f6991f.jpeg)

Are you up for a bigger challenge?

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<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [16 February 2022 10:56 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/13 "2022-02-16T10:56:37Z")

</div>

I never answer yes to questions like that, but maybe.

Mark this a solution (if it is) then make a new topic for any new questions. It will make it easier for people in future to find solutions.

---

<div class="post-metadata">

**Author:** ![WBr](https://avatars.discourse-cdn.com/v4/letter/w/b3f665/32.png) [@WBr](https://discourse.nodered.org/u/WBr)\
**Post date:** [16 February 2022 10:58 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/14 "2022-02-16T10:58:02Z")

</div>

Sure!

I Can't seem to send you a dm as your profile is hidden. How should I contact you?

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [2 March 2022 10:59 UTC](https://discourse.nodered.org/t/calculator-multiple-variable-coding-question/58422/15 "2022-03-02T10:59:01Z")

</div>

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