First array value not being accessed in Arduino sketch - arrays

Question

I'm creating a code that recreate's a clock without using a RTC module. I was busy adding in the days. The problem came when looping through the array. when the index==0, it gives a random form of char.
This is the code that doesn't work:
int theDayindex=0;
String weekDay[]={"maandag","dinsdag","woensdag","donderdag","vrijdag","zaterdag","zondag"};
String theDaydisplay=weekDay[theDayindex];
theDayindex++;
theDaydisplay=weekDay[theDayindex];
if(theDayindex>=6){
theDayindex=0;
}
I think the problem is that when you loop through the code, it does not detect 0 as an index. I'm not really familiar with the C language so it might work differently.
#include <Wire.h>
#include <hd44780.h>
#include <hd44780ioClass/hd44780_I2Cexp.h>
#include <dht.h>
#include <NewPing.h>
int page = 1;
int secs = 0;
int mins = 52;
int hors = 20;
int T;
int H;
int IRpin = 13;
int Timer = 0;
int theDayindex = 0;
String weekDay[] = {
"maandag",
"dinsdag",
"woensdag",
"donderdag",
"vrijdag",
"zaterdag",
"zondag"
};
String theDaydisplay = weekDay[theDayindex];
hd44780_I2Cexp lcd;
dht DHT;
NewPing sonar(11, 12, 400);
void setup() {
Serial.begin(9600);
lcd.begin(16, 2);
lcd.init();
lcd.backlight();
}
void loop() {
secs++;
Timer++;
theDayindex++;
theDaydisplay = weekDay[theDayindex];
if (theDayindex >= 6) {
theDayindex = 0;
}
Serial.println(theDayindex);
Serial.println(theDaydisplay);
unsigned int dstnc = sonar.ping_cm();
if (dstnc <= 30) {
lcd.backlight();
lcd.display();
Timer = 0;
page++;
}
if (secs >= 60) {
secs = 0;
mins++;
lcd.clear();
}
if (mins >= 60) {
hors++;
mins = 0;
secs = 0;
lcd.clear();
}
if (hors >= 24) {
hors = 0;
mins = 0;
secs = 0;
lcd.clear();
theDayindex++;
theDaydisplay = weekDay[theDayindex];
if (theDayindex >= 6) {
theDayindex = 0;
}
}
if (Timer >= 60) {
page = 1;
lcd.noBacklight();
lcd.noDisplay();
}
if (page == 1) {
lcd.clear();
lcd.setCursor(0, 2);
lcd.print(theDaydisplay);
lcd.setCursor(0, 0);
lcd.print(hors);
lcd.setCursor(2, 0);
lcd.print(":");
lcd.setCursor(3, 0);
lcd.print(mins);
lcd.setCursor(5, 0);
lcd.print(":");
lcd.setCursor(6, 0);
lcd.print(secs);
}
if (page == 2) {
int chk = DHT.read11(7);
H = DHT.humidity;
T = DHT.temperature;
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("Hum:");
lcd.setCursor(4, 0);
lcd.print(H);
lcd.setCursor(9, 0);
lcd.print("temp: ");
lcd.setCursor(14, 0);
lcd.print(T);
}
if (page >= 3) {
page = 1;
}
delay(955);
}

Answer 1

If the issue is the loop not accessing the first index, then the culprit is:
theDayindex++;
The theDayindex is first set to 0 but immediately incremented when the loop starts. So just move the index increments to the end of your loop.
#include <Wire.h>
#include <hd44780.h>
#include <hd44780ioClass/hd44780_I2Cexp.h>
#include <dht.h>
#include <NewPing.h>
int page = 1;
int secs = 0;
int mins = 52;
int hors = 20;
int T;
int H;
int IRpin = 13;
int Timer = 0;
int theDayindex = 0;
String weekDay[] = {
"maandag",
"dinsdag",
"woensdag",
"donderdag",
"vrijdag",
"zaterdag",
"zondag"
};
String theDaydisplay = weekDay[theDayindex];
hd44780_I2Cexp lcd;
dht DHT;
NewPing sonar(11, 12, 400);
void setup() {
Serial.begin(9600);
lcd.begin(16, 2);
lcd.init();
lcd.backlight();
}
void loop() {
theDaydisplay = weekDay[theDayindex];
if (theDayindex >= 6) {
theDayindex = 0;
}
Serial.println(theDayindex);
Serial.println(theDaydisplay);
unsigned int dstnc = sonar.ping_cm();
if (dstnc <= 30) {
lcd.backlight();
lcd.display();
Timer = 0;
page++;
}
if (secs >= 60) {
secs = 0;
mins++;
lcd.clear();
}
if (mins >= 60) {
hors++;
mins = 0;
secs = 0;
lcd.clear();
}
if (hors >= 24) {
hors = 0;
mins = 0;
secs = 0;
lcd.clear();
theDayindex++;
theDaydisplay = weekDay[theDayindex];
if (theDayindex >= 6) {
theDayindex = 0;
}
}
if (Timer >= 60) {
page = 1;
lcd.noBacklight();
lcd.noDisplay();
}
if (page == 1) {
lcd.clear();
lcd.setCursor(0, 2);
lcd.print(theDaydisplay);
lcd.setCursor(0, 0);
lcd.print(hors);
lcd.setCursor(2, 0);
lcd.print(":");
lcd.setCursor(3, 0);
lcd.print(mins);
lcd.setCursor(5, 0);
lcd.print(":");
lcd.setCursor(6, 0);
lcd.print(secs);
}
if (page == 2) {
int chk = DHT.read11(7);
H = DHT.humidity;
T = DHT.temperature;
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("Hum:");
lcd.setCursor(4, 0);
lcd.print(H);
lcd.setCursor(9, 0);
lcd.print("temp: ");
lcd.setCursor(14, 0);
lcd.print(T);
}
if (page >= 3) {
page = 1;
}
delay(955);
secs++;
Timer++;
theDayindex++;
}

Answer 2

As Stormix answared, you never use weekDay[0]. When theDaydisplay=weekDay[theDayindex] is executed for the first time, theDayIndex has already been incremented, so you are accessing weekDay[1]. Just changing the lines order should solve your problem.
int theDayindex=0;
String weekDay[]={"maandag","dinsdag","woensdag","donderdag","vrijdag","zaterdag","zondag"};
String theDaydisplay=weekDay[theDayindex];
theDaydisplay=weekDay[theDayindex];
theDayindex++;
if(theDayindex>=6){
theDayindex=0;
}