Error message of convert string to number

MIT App Inventor Help
1

I got "The operation * cannot accept the arguments: , [""], [1]" error message. This is what I used to convert barcode scanner result which is string to number. And I use "do it" to check, it works and is a number.
But AI Companion on my phone display above error message, and stop running.

2020-12-13_132928
2020-12-13_1329281410×179 42.1 KB

2

One of your scans is not returning a result:

image

You need to test for this before the calculation, and use the afterScan event block for each scan in turn

3

You are trying to display the result before it is avaliable...
Also why are you scanning twice?

Use the AfterScan event to display the result

Taifun

4

Thank you for reminding me that I may not scan correctly which creates"".

5

Thank you for reminding me to use AfterScan event, I will try to use that event as TIMAI2 also told me that .
My app is to create a referee for military strategy chess board game when playing covered. So that two players can play covered game without third person as a referee. When two pieces meet, just scan the QR code attached to each piece (that's why I need to scan twice) to determine who is stronger by color displayed on screen.

6

Thanks! Problem solved by using AfterScan event. I will publish this project to the Gallery for you to take look at it and you get the credit for your help :slight_smile:

George