Arduino array how values are stored, how this think is working

Projects Programming
1

Hi, I need little help with array, because something I didn’t understand.

Lets say we have 3 potentiometers, or 3 led or buttons. And we need to store the state of those.

For example let’s say we need to store the present value of a potentiometer.

The array will be

Int potentiometer [3] = {potensiometer1, potensiometer 2, potensiometer 3,};

In void loop we have the code that is reading the potentiometer value.

int potensiometer1 = analogRead(A0);

int potensiometer2 = analogRead(A1);.

int potensiometer3 = analogRead(A1);

the questions is how this values gos get stored to the array. Is automatic stored because array has the same name, how thinks work please.

2

No

In the case of your example the array has 3 elements

potentioneter[0]
potentioneter[1]
potentioneter[2]

So you would save a value like this

int potensiometer1 = analogRead(A0);
potentiometer[0] = potensiometer1 ;

or you could do

potentiometer[0] = analogRead(A0);
3

so is mean that inside [ ] the number you insert is store the valuw to that index. 0, 1, 2,
if you dont specify index in the [ ] what will happend?

4

Try it and see

5

and as you try things out, enable all warnings in the preference panel and try to write in potentiometer[3] (ie beyond the bounds of the array) to see what happens as well.

Good learning opportunity

6

if you mean to add more index

potentiometer[3] = analogRead(A0);

ok it will be error

7

I know I know not everyone has Google or even knows it exists so I Googled it for you C++ Arrays

2 Likes
8

last index in 3 element array is 2

0,1,2 - 3 elements. Why don’t you read on arrays first?

9

read the thread first :slight_smile:

I was the one to suggest that he tries that as a learning opportunity.

@tasoscy properly referred to the right indexes

10

i read my friend. and i understand.

11

i did my home work, and your asnwers was help full, i write this code, is a vu meter, it takes the midi cc and acording it light the led.

because i have 2 deferent row of led in the max7219 that i want to light up, i end up with this code, and i will like your oppinion, i did it corect or wrong. code is working

2 thinks that are not clear in my mind is this.

i have an array with 12 index.

lets take case 2. my logic is, if CC is 2, then case 2 will activate. now i have a four loop.
when i tell that (int i=2; ) ( i < 9; ) is equal to 2 < 9 till here i got it.

for (int i = 2; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }

here when i declare (vul[i], false.) my logic is that (i ) is 2 and this (i) is transfer to (vul[i], and it call the index number 1, that is 1 and it light the led no1

the next loop the( i ) equal to 3. so it call index no3 that is no 2, so led no2 is light up
and i assume the loop is exit when 9 < 9; it stop here?

take a look in case 9.
my logic here is that because i need to light leds in row no4 , but leds in row no2 not to turn off

my question here is that (i) should be 9 too? or 5 how i did it.. because i only light up 4 leds from the row now 4

case 2:
            for (int i = 2; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 2; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 3:
            for (int i = 3; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 3; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

#include "MIDIUSB.h"// Library from here https://github.com/FortySevenEffects/arduino_midi_library
#include "LedControl.h"

//pin 12 is connected to the DataIn
// pin 11 is connected to the CLK
// pin 10 is connected to LOAD
LedControl lc = LedControl(12, 11, 10, 1);
byte VU_MIDI_CH = 0;
byte vuLcc = 12;
int delaytime = 200;
unsigned int vul[12] = {0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3,};
unsigned int vul1[8] = {0, 1, 2, 3, 4, 5, 6, 7,};

int ccLastValue = 0;

//unsigned int Vuvaleu[7] = {0, 0, 0, 0, 0, 0, 0,};
void setup() {

  lc.shutdown(0, false);

  lc.setIntensity(0, 8);

  lc.clearDisplay(0);

  Serial.begin(115200);
  lc.setLed (0, 7, 1, true); // turn 1 led on to see if the code is working

  //all leds in row 2 are turn on one by one

  for (int i = 0; i < 8; i++) {

    lc.setLed(0, 2, vul[i], true);
    delay(delaytime);
  }

  //all leds in row 6 turn on one by one

  for (int i = 0; i < 8; i++) {

    lc.setLed(0, 6, vul1[i], true);
    delay(delaytime);
  }
  lc.clearDisplay(0);

}




void loop() {
  midiEventPacket_t rx = MidiUSB.read();

  switch (rx.header) {
    case 0:
      break; //No pending events

    //  case 0x9:
    //      handleNoteOn(
    //        rx.byte1 & 0xF,  //channel
    //        rx.byte2,        //pitch
    //        rx.byte3         //velocity
    //      );
    //      break;

    //    case 0x8:
    //      handleNoteOff(
    //        rx.byte1 & 0xF,  //channel
    //        rx.byte2,        //pitch
    //        rx.byte3         //velocity
    //      );
    //      break;

    case 0xB:
      vumeter(
        rx.byte1 & 0xF,  //channel
        rx.byte2,        //cc
        rx.byte3         //value
      );
      break;


  }
}

void vumeter(byte channel, byte number, byte value) {

  int value_ = value;

  if (value_ != ccLastValue) {

    if (channel == VU_MIDI_CH) {

      if (number == vuLcc ) {


        switch (value_) {
//led in row 2 are light acording to the case
          
          case 0:

            for (int i = 0; i < 12; i++) {
              lc.setLed(0, 2, vul[i], false);
              lc.setLed(0, 4, vul[i], false);
            }

            break;

          case 1:
            for (int i = 1; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 1; i++) {
              lc.setLed(0, 2, vul[0], true);
            }
            break;


          case 2:
            for (int i = 2; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 2; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 3:
            for (int i = 3; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 3; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 4:

            for (int i = 4 ; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 4; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 5:
            for (int i = 5; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 5; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 6:
            for (int i = 6; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 6; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 7:
            for (int i = 7; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 7; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

          case 8:
            for (int i = 8; i < 9; i++) {
              lc.setLed(0, 2, vul[i], false);
            }
            for (int i = 0; i < 8; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            break;

            // led in the row 4 are light acording to the case, but leds in the row 2 should stay on

          case 9:
            for (int i = 0; i < 9; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            for (int i = 0; i < 5; i++) {
              lc.setLed(0, 4, vul[i], false);
            }
            for (int i = 0; i < 0; i++) {
              lc.setLed(0, 4, vul[i], true);
            }
            break;

          case 10:
            for (int i = 0; i < 9; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            for (int i = 1; i < 9; i++) {
              lc.setLed(0, 4, vul[i], false);
            }
            for (int i = 0; i < 1; i++) {
              lc.setLed(0, 4, vul[i], true);
            }
            break;

          case 11:
            for (int i = 0; i < 9; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            for (int i = 2; i < 9; i++) {
              lc.setLed(0, 4, vul[i], false);
            }
            for (int i = 0; i < 2; i++) {
              lc.setLed(0, 4, vul[i], true);
            }
            break;

          case 12:
            for (int i = 0; i < 9; i++) {
              lc.setLed(0, 2, vul[i], true);
            }
            for (int i = 3; i < 9; i++) {
              lc.setLed(0, 4, vul[i], false);
            }
            for (int i = 0; i < 3; i++) {
              lc.setLed(0, 4, vul[i], true);
            }
            break;
        }
        ccLastValue = value;
      }
    }
  }
}

void noteOff(byte channel, byte pitch, byte velocity) {
  midiEventPacket_t noteOff = {0x08, 0x80 | channel, pitch, velocity};
  MidiUSB.sendMIDI(noteOff);
}


void controlChange(byte channel, byte control, byte value) {
  midiEventPacket_t event = {0x0B, 0xB0 | channel, control, value};
  MidiUSB.sendMIDI(event);

}

void noteOn(byte channel, byte pitch, byte velocity) {
  midiEventPacket_t noteOn = {0x09, 0x90 | channel, pitch, velocity};
  MidiUSB.sendMIDI(noteOn);
}
12

I don't know the LedControl library - if it works ...

i will go from 2 to 8 inclusive when the for loop runs and thus when i is 2, you'll access vol[2] which is the third element in the array.

13

When i is 2 the value at that location in the vul array 2, not 1

unsigned int vul[12] = {0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3,};

Remember that the array index start at 0, not 1

The vul1 array looks redundant because the value at index 0 is 0, at index 1 is 1, at index 2 is 2 and so on so you might just as well use the index values as the value in the array

14

yes i think i understand it, i assume i didnt write it correct in post.

index 0 is no 1 when you call index 0 and index 1 is no 2 when you call index 1?

this is the correct

15

to my eyes, is working perfect so far, i dont know, if my code is been write in the correct way considering the case fuction..

i dont know if i use the correct logic to over come the problem, when leds in deferend row will need to start to blink.

16

if this is what you mean:

  • index 0 is the first entry of the array
  • index 1 is the second entry of the array
  • index 2 is the third entry of the array
  • ...

then you are correct

17

this is how i understand it

mr ukhelibob said

When i is 2 the value at that location in the vul array 2, not 1
he confuse me.

o i think here i miss understand.

there is no (i=0)

i=1 is mean it call index 1, with the value of 0
i=2 is mean it call index 2 with value 1

18

is this bellow corect? if (i=0) i think nothink will happend.

because (i=0; 0 < 0; i++) nothing happen, am i correct??

case 9:
            for (int i = 0; i < 9; i++) {
              lc.setLed(0, 0, vul[i], true);
            }
            for (int i = 0; i < 9; i++) {
              lc.setLed(0, 1, vul[i], false);
            }
            for (int i = 0; i < 0; i++) {
              lc.setLed(0, 1, vul[i], true);
            }
            break;
19

@UKHeliBob is correct

image
image1280×148 19.9 KB

the value at index 2 (the third entry) is 2
or in C++ vul[2) == 2 ➜ is true

20

Try this

void setup()
{
  Serial.begin(115200);
  byte array[] = {100, 101, 102, 103};
  for (int c = 0; c < 4; c++)
  {
    Serial.print("At index ");
    Serial.print(c);
    Serial.print(" the value is ");
    Serial.println(array[c]);
  }
}

void loop()
{
}