Show result on the chart

Hello everyone. I am learning MQL5, I’m having an issue, and I wonder if someone here could help me.
I would like to calculate the difference between the current closing price and the twenty simple moving average and then show the result on the chart. 
I did this and it has been correctly compiled, but it always shows 0.0000. 
Please, can someone check my code and figure out where the error is ?
DIF.JPG  19 kb
code.JPG  78 kb
Res.png  6 kb
  1. Don't post pictures of code, they are generally too hard to read.

    Please edit your (original) post and use the CODE button (or Alt+S)! (For large amounts of code, attach it.)
              General rules and best pratices of the Forum. - General - MQL5 programming forum (2019)
              Messages Editor

  2. Perhaps you should read the manual, especially the examples.
       How To Ask Questions The Smart Way. (2004)
          How To Interpret Answers.
             RTFM and STFW: How To Tell You've Seriously Screwed Up.

    They all (including iCustom) return a handle (an int). You get that in OnInit. In OnTick/OnCalculate (after the indicator has updated its buffers), you use the handle, shift and count to get the data.
              Technical Indicators - Reference on algorithmic/automated trading language for MetaTrader 5
              Timeseries and Indicators Access / CopyBuffer - Reference on algorithmic/automated trading language for MetaTrader 5
              How to start with MQL5 - General - MQL5 programming forum - Page 3 #22 (2020)
              How to start with MQL5 - MetaTrader 5 - General - MQL5 programming forum - Page 7 #61 (2020)
              MQL5 for Newbies: Guide to Using Technical Indicators in Expert Advisors - MQL5 Articles (2010)
              How to call indicators in MQL5 - MQL5 Articles (2010)

  3. You did not set your array (Diff) direction.

    To determine the indexing direction of time[], open[], high[], low[], close[], tick_volume[], volume[] and spread[], call ArrayGetAsSeries(). In order not to depend on default values, you should unconditionally call the ArraySetAsSeries() function for those arrays, which are expected to work with.
              Event Handling Functions - Functions - Language Basics - MQL4 Reference

  4. PRICE_CLOSE is constant (for iMA), not a value.