For my project I am using a gps module to get coordinates to send via Bluetooth BLE to MIT app inventor. The gps puts out coordinates as a double but I need to send them as a string. How do I do this? I do not really know how to code that well. Thank you for your help (any advice is welcomed)
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On most Arduinos double and float are the same thing, Floats are stored in 4 bytes.
The dtostrf() function is one way to convert a float to a string (null terminated character array).
The source data from the GPS module is unlikely to be a double.
I'd start looking closer to that interface.
On ATmega based Arduinos a float is the same as a double in size/precision. Sometimes the library uses the double type but it's not helping on that hardware.
To convert a number easily to a nicely formatted string: use the sprintf() function.