How do I create a signal for indicator?

[TJFB]

Hi,

I have a 0 line indicator; I’d like to to produce an alert when it crosses the 0 line. How do I do this?

[William Roeder]

1. If you have the code, test for a cross and issue the alert.

   double aPrev = …, aCurr = …;
   bool   wasUp = aPrev > 0,
           isUp = aCurr > 0,
          isCross = isUp != wasUp;

2. Otherwise, create an indicator that reads it using iCustom.
             Detailed explanation of iCustom - MQL4 programming forum