xcode-select: error: tool 'genstrings' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

I'm using Xcode 8 on MacOS Sierra to develop an iOS application just for learning purpose. I run the command below to create a strings table file for a view controller class but got the error.

genstrings MapViewController.swift

I can't find Xcode in Applications directory. I don't know why as i'm new to it, and I don't want to find out now. However, I accidentally fixed it myself.

1. Open Xcode and go to Xcode preferences by pressing command + ,
2. Select Locations tab and select "Xcode 8.3.3 (8E3004b)" from the "Command Line Tools" combo box.