Скачать или смотреть MQL4 Tutorial Bootcamp2 - 3 Import the new MQ4 Module

https://mql4tutorial.com/?s=expert

In the last part, you have created your first MQ4 module, but I’ve made a little mistake. I wanted to include the file in the main expert advisor but I got this error because I forgot the double quotes. Now, the import should work. Right at the start, in the OnTick function, we are going to call our new created CheckTrend function. It will return a double value. What does it mean?
You can look up data types in the MQL4 reference. The data type double is for floating point values and that’s exactly what we need. Now, we click the Compile button and we have no errors and no warnings. One more thing, if I change anything in my systems, I will save them with a new name. Very often, I will use the date. Let’s hit the F4 key again and choose the new EA. Okay, it works.