Sorry about a newbie. 1. what mening of:

    if(Xstr[XstrLength-1] != '|'){
      Xstr[XstrLength] = '|';
      Xstr[XstrLength+1] = '\0';
  1. the setup: char Xstr[60]; what means? and then: itoa(Yint,Ystr,10);


#include <VirtualWire.h>

//gamepad setup
int up_button = 2;
int down_button = 4;
int left_button = 5;
int right_button = 3;
int start_button = 6;
int select_button = 7;
int joystick_button = 8;
int joystick_axis_x = A0;
int joystick_axis_y = A1;
int buttons[] = {up_button, down_button, left_button, right_button, start_button, select_button, joystick_button};

void setup()

    //gamepad setup
    for (int i; i < 7; i++)
        pinMode(buttons[i], INPUT);
        digitalWrite(buttons[i], HIGH);

    Serial.begin( 9600 );

    //transmitter setup
    vw_set_tx_pin(12);          // Sets pin D12 as the TX pin
    vw_set_ptt_inverted(true);  // Required for DR3100
    vw_setup(2000);             // Bits per sec

int counter = 0;

int Xint;
int Yint;

char Xstr[60];
char Ystr[60];

void loop()
    // Read and store Sensor  data
    Xint = analogRead(joystick_axis_x);
    Yint = analogRead(joystick_axis_y);

    // Convert integer data to Char array directly 

    int XstrLength = String(Xstr).length();

    if(Xstr[XstrLength-1] != '|'){
        Xstr[XstrLength] = '|';
        Xstr[XstrLength+1] = '\0';

    char combinedArray[String(Xstr).length() + String(Ystr).length() + 1];
    sprintf(combinedArray, "%s%s", Xstr, Ystr);

    vw_send((uint8_t *)combinedArray, strlen(combinedArray));
    vw_wait_tx(); // Wait until the whole message is gone 


  1. This adds some end of string characters.

    if(Xstr[XstrLength-1] != '|'){ Xstr[XstrLength] = '|'; Xstr[XstrLength+1] = '\0'

First it checks if Xstr last character is a '|', if not: Place a | directly after the last character And append a '\0', which is a symbol to 'end' a string

A string in C/C++ is normally build up like this, e.g. "Hello" contains of the bytes:

'H', 'e', 'l', 'l', 'o', \0

Where each of the above are ASCII characters/values and the last \0 a 0 byte.

  1. char Xstr[60]; defines a character array (string) that can contain 60 characters. Note however, that the ending \0 also needs to be in this string, so you can actually only put 59 characters inside.

  2. itoa(Yint,Ystr,10); converts Yint which is an integer value to a string (where each digit has each own byte), and 10 is the length.

  • Thank you Michel Keijzers. I confused with char Xstr[60] and itoa(Yint,Ystr,10), actually they not same thing. – laoadam Mar 15 at 22:14
  • Gladly done, If the answer helps you, please consider upvote and accept my answer. – Michel Keijzers Mar 15 at 22:43
  • HI, when used a MCP4261, there is function "digitalPotWrite" , can I use "digitalWrite" replace it? Thanks. – laoadam Mar 16 at 20:05
  • Because the "digitalPotWrite" need be void definition, can't be used inside setup. – laoadam Mar 16 at 20:17
  • digitalPotWrite is a function to communicate with the MCP4261 over SPI. digitalWrite is a function to set an IO pin HIGH or LOW. The two have nothing at all to do with each other. – Majenko Mar 18 at 21:56

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