please explain the sketch attached

Question

Sorry about a newbie. 1. what mening of:

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

2. the setup: char Xstr[60]; what means? and then: itoa(Yint,Ystr,10);

Code:

#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 
    itoa(Yint,Ystr,10);
    itoa(Xint,Xstr,10);

    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 

    Serial.println(combinedArray);

}

Answer 1

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.

2. 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.

3. 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.