user196: I downloaded Arduino code from this: https://github.com/BabyWrassler/MissionControl/ Github, and got the  error message below.
It is designed to work with a Raspberry Pi, and I installed the two Adafruit libraries.  I also have not hooked it up to either the Pi, or the two Adafruit devices, but that is partly because I cannot get it to run without the error message.
Update:
Here is what was highlighted: 
Adafruit_LEDBackpack matrixA = Adafruit_LEDBackpack();
The orange bar says:
    Variable or field ‘matrixOff‘ declared void
I cannot tell what of the following was from before, but here is the entire console log:
    mcDesk.ino:2:53: error: Adafruit_LEDBackpack.h: No such file or directory
    mcDesk.ino:3:45: error: Adafruit_GFX.h: No such file or directory
    mcDesk:11: error: variable or field 'matrixOff' declared void
    mcDesk:11: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:11: error: expected primary-expression before 'buffer'
    mcDesk:12: error: variable or field 'ledOn' declared void
    mcDesk:12: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:12: error: expected primary-expression before 'buffer'
    mcDesk:12: error: expected primary-expression before 'cat'
    mcDesk:12: error: expected primary-expression before 'an'
    mcDesk:13: error: variable or field 'ledOff' declared void
    mcDesk:13: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:13: error: expected primary-expression before 'buffer'
    mcDesk:13: error: expected primary-expression before 'cat'
    mcDesk:13: error: expected primary-expression before 'an'
    mcDesk:14: error: variable or field 'dispMat' declared void
    mcDesk:14: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:14: error: expected primary-expression before 'buffer'
    mcDesk:17: error: variable or field 'threeDigitDisp' declared void
    mcDesk:17: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:17: error: expected primary-expression before 'buffer'
    mcDesk:17: error: expected primary-expression before 'cats'
    mcDesk:17: error: expected primary-expression before 'ans'
    mcDesk:17: error: expected primary-expression before 'number'
    mcDesk:18: error: variable or field 'digitDisp' declared void
    mcDesk:18: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:18: error: expected primary-expression before 'buffer'
    mcDesk:18: error: expected primary-expression before 'pos'
    mcDesk:18: error: expected primary-expression before 'cat'
    mcDesk:18: error: expected primary-expression before 'an'
    mcDesk:18: error: expected primary-expression before 'num'
    mcDesk:23: error: variable or field 'switchBars' declared void
    mcDesk:23: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:23: error: expected primary-expression before 'buffer'
    mcDesk:23: error: expected primary-expression before 'grphCats'
    mcDesk:23: error: expected primary-expression before 'grphAns'
    mcDesk:23: error: expected primary-expression before 'cmnd'
    mcDesk:23: error: expected primary-expression before 'offset'
    mcDesk:24: error: variable or field 'barDisp' declared void
    mcDesk:24: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:24: error: expected primary-expression before 'buffer'
    mcDesk:24: error: expected primary-expression before 'grphCats'
    mcDesk:24: error: expected primary-expression before 'grphAns'
    mcDesk:24: error: expected primary-expression before 'pos'
    mcDesk:24: error: expected primary-expression before 'offset'
    mcDesk:25: error: variable or field 'cBarDisp' declared void
    mcDesk:25: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:25: error: expected primary-expression before 'buffer'
    mcDesk:25: error: expected primary-expression before 'grphCats'
    mcDesk:25: error: expected primary-expression before 'grphAns'
    mcDesk:25: error: expected primary-expression before 'pos'
    mcDesk:25: error: expected primary-expression before 'offset'
    mcDesk:11: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:12: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:13: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:14: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:15: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk.ino: In function 'void decodeCommand()':
    mcDesk:193: error: 'matrixE' was not declared in this scope
    mcDesk:193: error: 'ledOn' was not declared in this scope
    mcDesk:199: error: 'matrixE' was not declared in this scope
    mcDesk:199: error: 'ledOff' was not declared in this scope
    mcDesk:204: error: 'matrixC' was not declared in this scope
    mcDesk:204: error: 'cBarDisp' was not declared in this scope
    mcDesk.ino: In function 'void allMatrixOff()':
    mcDesk:213: error: 'matrixA' was not declared in this scope
    mcDesk:213: error: 'matrixOff' was not declared in this scope
    mcDesk:214: error: 'matrixB' was not declared in this scope
    mcDesk:215: error: 'matrixC' was not declared in this scope
    mcDesk:216: error: 'matrixD' was not declared in this scope
    mcDesk:217: error: 'matrixE' was not declared in this scope
    mcDesk.ino: At global scope:
    mcDesk:220: error: variable or field 'matrixOff' declared void
    mcDesk:220: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:220: error: expected primary-expression before 'buffer'


user84: It seems to me that those Adafruit libraries were not correctly installed on your PC or your sketch.
In addition to downloading and installing the library onto the Arduino library directory (on Windows, that's normally C:\Users\UserName\Documents\Arduino\libraries), when you want to use that library with Arduino IDE, you must add the library for your sketch with the menu command "Sketch -> Import Library..."
Important note: it seems just adding #include "library.h" does not work with Arduino IDE, you absolutely need to use the menu.

196: <p>I downloaded Arduino code from this: <a href="https://github.com/BabyWrassler/MissionControl/" rel="nofollow">https://github.com/BabyWrassler/MissionControl/</a> Github, and got the  error message below.</p>

<p>It is designed to work with a Raspberry Pi, and I installed the two Adafruit libraries.  I also have not hooked it up to either the Pi, or the two Adafruit devices, but that is partly because I cannot get it to run without the error message.</p>

<p>Update:
Here is what was highlighted: 
<code>Adafruit_LEDBackpack matrixA = Adafruit_LEDBackpack();</code>
The orange bar says:
    Variable or field ‘matrixOff‘ declared void
I cannot tell what of the following was from before, but here is the entire console log:</p>

<pre><code>    mcDesk.ino:2:53: error: Adafruit_LEDBackpack.h: No such file or directory
    mcDesk.ino:3:45: error: Adafruit_GFX.h: No such file or directory
    mcDesk:11: error: variable or field 'matrixOff' declared void
    mcDesk:11: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:11: error: expected primary-expression before 'buffer'
    mcDesk:12: error: variable or field 'ledOn' declared void
    mcDesk:12: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:12: error: expected primary-expression before 'buffer'
    mcDesk:12: error: expected primary-expression before 'cat'
    mcDesk:12: error: expected primary-expression before 'an'
    mcDesk:13: error: variable or field 'ledOff' declared void
    mcDesk:13: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:13: error: expected primary-expression before 'buffer'
    mcDesk:13: error: expected primary-expression before 'cat'
    mcDesk:13: error: expected primary-expression before 'an'
    mcDesk:14: error: variable or field 'dispMat' declared void
    mcDesk:14: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:14: error: expected primary-expression before 'buffer'
    mcDesk:17: error: variable or field 'threeDigitDisp' declared void
    mcDesk:17: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:17: error: expected primary-expression before 'buffer'
    mcDesk:17: error: expected primary-expression before 'cats'
    mcDesk:17: error: expected primary-expression before 'ans'
    mcDesk:17: error: expected primary-expression before 'number'
    mcDesk:18: error: variable or field 'digitDisp' declared void
    mcDesk:18: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:18: error: expected primary-expression before 'buffer'
    mcDesk:18: error: expected primary-expression before 'pos'
    mcDesk:18: error: expected primary-expression before 'cat'
    mcDesk:18: error: expected primary-expression before 'an'
    mcDesk:18: error: expected primary-expression before 'num'
    mcDesk:23: error: variable or field 'switchBars' declared void
    mcDesk:23: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:23: error: expected primary-expression before 'buffer'
    mcDesk:23: error: expected primary-expression before 'grphCats'
    mcDesk:23: error: expected primary-expression before 'grphAns'
    mcDesk:23: error: expected primary-expression before 'cmnd'
    mcDesk:23: error: expected primary-expression before 'offset'
    mcDesk:24: error: variable or field 'barDisp' declared void
    mcDesk:24: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:24: error: expected primary-expression before 'buffer'
    mcDesk:24: error: expected primary-expression before 'grphCats'
    mcDesk:24: error: expected primary-expression before 'grphAns'
    mcDesk:24: error: expected primary-expression before 'pos'
    mcDesk:24: error: expected primary-expression before 'offset'
    mcDesk:25: error: variable or field 'cBarDisp' declared void
    mcDesk:25: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:25: error: expected primary-expression before 'buffer'
    mcDesk:25: error: expected primary-expression before 'grphCats'
    mcDesk:25: error: expected primary-expression before 'grphAns'
    mcDesk:25: error: expected primary-expression before 'pos'
    mcDesk:25: error: expected primary-expression before 'offset'
    mcDesk:11: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:12: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:13: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:14: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk:15: error: 'Adafruit_LEDBackpack' does not name a type
    mcDesk.ino: In function 'void decodeCommand()':
    mcDesk:193: error: 'matrixE' was not declared in this scope
    mcDesk:193: error: 'ledOn' was not declared in this scope
    mcDesk:199: error: 'matrixE' was not declared in this scope
    mcDesk:199: error: 'ledOff' was not declared in this scope
    mcDesk:204: error: 'matrixC' was not declared in this scope
    mcDesk:204: error: 'cBarDisp' was not declared in this scope
    mcDesk.ino: In function 'void allMatrixOff()':
    mcDesk:213: error: 'matrixA' was not declared in this scope
    mcDesk:213: error: 'matrixOff' was not declared in this scope
    mcDesk:214: error: 'matrixB' was not declared in this scope
    mcDesk:215: error: 'matrixC' was not declared in this scope
    mcDesk:216: error: 'matrixD' was not declared in this scope
    mcDesk:217: error: 'matrixE' was not declared in this scope
    mcDesk.ino: At global scope:
    mcDesk:220: error: variable or field 'matrixOff' declared void
    mcDesk:220: error: 'Adafruit_LEDBackpack' was not declared in this scope
    mcDesk:220: error: expected primary-expression before 'buffer'
</code></pre>
 84: <p>It seems to me that those Adafruit libraries were not correctly installed on your PC or your sketch.</p>

<p>In addition to downloading and installing the library onto the Arduino library directory (on Windows, that's normally <code>C:\Users\UserName\Documents\Arduino\libraries</code>), when you want to use that library with Arduino IDE, you must add the library for your sketch with the menu command "<strong>Sketch -> Import Library...</strong>"</p>

<p><strong>Important note</strong>: it seems just adding <code>#include "library.h"</code> does not work with Arduino IDE, you absolutely need to use the menu.</p>
