Printing to Screen

I've been fooling around with programming EAs, making simple MA and other indicator based trading systems. However, I don't know how to approach making an indicator.

Basically, i don't know how to output to the UI. When X and Y return TRUE, i want to print in the upper left corner of the chart. I've seen this done in other indicators, i must be missing something.

On a related note, is there a way to define a condition and have the indicator return which currency pairs return TRUE? I didn't think MT4 provided such functionality, but perhaps someone knows something.

Thanks

Use the Comment function

Comment("Hello User");

As far as your second question, use Globalvariables which can be read by any indicator or EA. Although global variables are only of type double you can assign them a 1 for true or a 0 for false. Then have the ea read each one to determine which is true.

string myglobalvariable;
myglobalvariable=Symbol()+"trueornot";
GlobalVariableSet(myglobalvariable,1);

By using the symbol function you create a unique global variable for each currency pair and you can then request that value by using the GlobalVariableGet function.