Change a global variable in an indicator by an expert

[Jo Jomax]

The function Oncalculate() can not be used in an expert. So we have to create our indicator separately from our expert and run both the expert and the indicator on the chart. I have a global variable in my indicator(that I wrote it in metaeditor) and I want to change the amount of this variable when a specific global variable in my expert is changed. Is it possible?

[Zaky Hamdoun]

Hello!

Use terminal global variables, with the functions such as GlobalVariableSet(), GlobalVariableGet() and so on. 

https://www.mql5.com/en/docs/globals

[Fernando Carreiro]

1. When calling a custom Indicator, from an Expert Advisor via the iCustom() function, one can pass it parameters to define how it should function.
2. Global Terminal Variables can be created, accessed and modified from any and all MQL programmes running on the terminal, be they Indicators, Expert Advisors, Scripts or Services. Which means they can be used as a type of Interprocess Communication method.
   
3. Just because the OnCalculate() event is not handled by Expert Advisors (EAs), does not mean you can't implement something equivalent in EAs, purely for calculations without graphical output.
4. EAs don't have "eyes" and don't need visual feedback. One can easily carry out all calculations in the EA itself without depending on Indicators, if one so wishes to do that.

[Jo Jomax]

Fernando Carreiro #:

1. When calling a custom Indicator, from an Expert Advisor via the iCustom() function, one can pass it parameters to define how it should function.
2. Global Terminal Variables can be created, accessed and modified from any and all MQL programmes running on the terminal, be they Indicators, Expert Advisors, Scripts or Services. Which means they can be used as a type of Interprocess Communication method.
   
3. Just because the OnCalculate() event is not handled by Expert Advisors (EAs), does not mean you can't implement something equivalent in EAs, purely for calculations without graphical output.
4. EAs don't have "eyes" and don't need visual feedback. One can easily carry out all calculations in the EA itself without depending on Indicators, if one so wishes to do that.

This is excellent. Thank you very much for this complete answer.