View source for How to Add Libraries to Arduino/libraries

==Introduction==
When you run the code, you may often encounter such problem as below.
<pre>
G:\Kit Code\Sensor Kit V2.0 for Arduino\Lesson 1 Display by I2C LCD1602\code\I2C_LCD1602\I2C_LCD1602.ino:3:31: fatal error: LiquidCrystal_I2C.h: No such file or directory

 #include <LiquidCrystal_I2C.h>
                               ^
compilation terminated.
</pre>

Using library Wire at version 1.0 in folder: C:\Program Files\Arduino\hardware\arduino\avr\libraries\Wire 
 exit status 1
 Error compiling for board Arduino/Genuino Mega or Mega 2560.
<br>[[File:How-1.png]]<br>
It may be the LiquidCrystal_I2C.h, but it also may be other .h files. “LiquidCrystal_I2C.h: No such file or directory” means this LiquidCrystal_I2C library can't be found when the Arduino IDE is running. Then, you need to add this library yourself.
==What is Library?==
Library, gathering some Function definitions and Header files, usually contains two files: .h (header file, including function statement, Macro definition, structure definition, etc.) and .cpp (execution file, with function implementation, variable definition, etc.). When you are in need of using a function in Library, you just need to add header file (#include <LiquidCrystal_I2C.h>), and then call that function. This can make your code more concise. <br>

If you don't want to use Library, you can write that function's definition in the code directly. However, such code will be too long and inconvenient to read.
<br>
When you want to know some function's functionality, you can search it in all code by Ctrl+F. If only an empty function is found, with no main body, it means that this function was called from a library. Then you can search it in library. 
<br>[[File:How-2.png]]<br>
==Add libraries==
We have learned library's functions above. Now let's move on to how to add a library. There are two methods to add the library.
===Method 1===
Directly import library in Arduino IDE (take LiquidCrystal_I2C as an example below). Advantage for this method is easy to understand and operate, but its disadvantage is that only one library can be imported at a time. So it is not so convenient when multiple libraries need to be imported.
'''Step 1:''' Open Arduino IDE, click '''Sketch''' -> '''Include Library''' -> '''Add .ZIP Library'''  
<br>[[File:How-3.png]]<br>
'''Step 2:''' Find Sensor Kit V2.0 for Arduino\Library\LiquidCrystal_I2C, click '''Open'''.
<br>[[File:How-4.png]]<br>
'''Step 3:''' When you see the highlighted message below, it means you have added the library successfully. Please use the same method to add other libraries then.
<br>[[File:How-5.png]]<br>
 
===Method 2===
Directly copy the library to libraries/Arduino path. This method can enable you to copy all libraries and add them at a time, but the drawback is that it is difficult to find libraries/Arduino.
'''Step 1:''' Click '''File''' -> '''Preferences'''
<br>[[File:How-6.png]]<br>
'''Step 2:''' The highlighted part below is the path where the libraries file lies. 
<br>[[File:How-7.png]]<br>
'''Step 3:''' Copy all libraries in the path of Sensor Kit V2.0 for Arduino\Library\.
<br>[[File:How-8.png]]<br>

'''Step 4:''' Go to the path you just saw in Arduino IDE. You will see there is a Libraries file. Please click to open it.
<br>[[File:How-9.png]]<br>
Step 5 Paste them then, and they will be in this file. Close the IDE you just opened, and re-open it. It will be able to be compiled successfully.