Also: What did you do so far?
It's always a good starting point to make it running as "normal" R - code before you translate it into a shiny app.
- First you need a list of "allowed" codes,
- then you need to grab the data (from the internet?)
- maybe clean-up the data (extract the last day)
- plot the data (acutally, the "closing price for the day" is just a number, so not so much to show. Or do you want to show the chart of the day? Or the closing price of the last 7 (or so) days?)
When you have more specific questions we are happy to help. But you have to show you already started your work.