gavmac00/arduino-docs huggingface dataset:
const
          [Variable Scope & Qualifiers]
          
Description
The const keyword stands for constant. It is a variable qualifier that modifies the behavior of the variable, making a variable "read-only". This means that the variable can be used just as any other variable of its type, but its value cannot be changed. You will get a compiler error if you try to assign a value to a const variable.
Constants defined with the const keyword obey the rules of variable scoping that govern other variables. This, and the pitfalls of using #define, makes the const keyword a superior method for defining constants and is preferred over using #define.
Example Code
const float pi = 3.14;
float x;
// ....
x = pi * 2; // it's fine to use consts in math
pi = 7;     // illegal - you can't write to (modify) a constant
Notes and Warnings
#define or const
Language
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Reference
            >  Language
            >  Variables
            >  Variable scope qualifiers
            > Scope
          
scope
          [Variable Scope & Qualifiers]
          
Description
Variables in the C++ programming language, which Arduino uses, have a property called scope. This is in contrast to early versions of languages such as BASIC where every variable is a global variable.
A global variable is one that can be seen by every function in a program. Local variables are only visible to the function in which they are declared. In the Arduino environment, any variable declared outside of a function (e.g. setup(), loop(), etc. ), is a global variable.
When programs start to get larger and more complex, local variables are a useful way to insure that only one function has access to its own variables. This prevents programming errors when one function inadvertently modifies variables used by another function.
It is also sometimes handy to declare and initialize a variable inside a for loop. This creates a variable that can only be accessed from inside the for-loop brackets.
Example Code
int gPWMval;  // any function will see this variable
void setup() {
  // ...
}
void loop() {
  int i;    // "i" is only "visible" inside of "loop"
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Reference
            >  Language
            >  Variables
            >  Variable scope qualifiers
            > Static
          
static
          [Variable Scope & Qualifiers]
          
Description
The static keyword is used to create variables that are visible to only one function. However unlike local variables that get created and destroyed every time a function is called, static variables persist beyond the function call, preserving their data between function calls.
Variables declared as static will only be created and initialized the first time a function is called.
Example Code
/* RandomWalk
  Paul Badger 2007
  RandomWalk wanders up and down randomly between two
  endpoints. The maximum move in one loop is governed by
  the parameter "stepsize".
  A static variable is moved up and down a random amount.
  This technique is also known as "pink noise" and "drunken walk".
*/
#define randomWalkLowRange -20
#define randomWalkHighRange 20
int stepsize;
int thisTime;
void setup() {
  Serial.begin(9600);
}
void loop() {
  //  test randomWalk function
  stepsize = 5;
  thisTime = randomWalk(stepsize);
  Serial.println(thisTime);
  delay(10);
}
int randomWalk(int moveSize) {
delay(10);
}
int randomWalk(int moveSize) {
  static int place; // variable to store value in random walk - declared static so that it stores
  // values in between function calls, but no other functions can change its value
  place = place + (random(-moveSize, moveSize + 1));
  if (place < randomWalkLowRange) {                               // check lower and upper limits
    place = randomWalkLowRange + (randomWalkLowRange - place);    // reflect number back in positive direction
  }
  else if (place > randomWalkHighRange) {
    place = randomWalkHighRange - (place - randomWalkHighRange);  // reflect number back in negative direction
  }
  return place;
}
See also
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Bytecast
          
byte()
          [Conversion]
          
Description
Converts a value to the byte data type.
Syntax
byte(x)
(byte)x (C-style type conversion)
Parameters
x: a value. Allowed data types: any type.
Returns
Data type: byte.
See also
LANGUAGE byte
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Wordcast
          
word()
          [Conversion]
          
Description
Converts a value to the word data type.
Syntax
word(x)
word(h, l)
(word)x (C-style type conversion)
Parameters
x: a value. Allowed data types: any type.
Language
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Libraries
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Glossary
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Intcast
          
int()
          [Conversion]
          
Description
Converts a value to the int data type.
Syntax
int(x)
(int)x (C-style type conversion)
Parameters
x: a value. Allowed data types: any type.
Returns
Data type: int.
See also
LANGUAGE int
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Charcast
          
char()
          [Conversion]
          
Description
Converts a value to the char data type.
Syntax
char(x)
(char)x (C-style type conversion)
Parameters
x: a value. Allowed data types: any type.
Returns
Data type: char.
See also
LANGUAGE char
Language
functions
variables
structure
Libraries
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Glossary
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Unsignedlongcast
          
(unsigned long)
          [Conversion]
          
Description
Converts a value to the unsigned long data type.
Syntax
(unsigned long)x
Parameters
x: a value of any type
Returns
unsigned long
See also
LANGUAGE unsigned long
Language
functions
variables
structure
Libraries
IoT Cloud API
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Floatcast
          
float()
          [Conversion]
          
Description
Converts a value to the float data type.
Syntax
float(x)
(float)x (C-style type conversion)
Parameters
x: a value. Allowed data types: any type.
Returns
Data type: float.
Notes and Warnings
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variables
structure
Libraries
IoT Cloud API
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Longcast
          
long()
          [Conversion]
          
Description
Converts a value to the long data type.
Syntax
long(x)
(long)x (C-style type conversion)
Parameters
x: a value. Allowed data types: any type.
Returns
Data type: long.
See also
LANGUAGE long
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Conversion
            > Unsignedintcast
          
(unsigned int)
          [Conversion]
          
Description
Converts a value to the unsigned int data type.
Syntax
(unsigned int)x
Parameters
x: a value of any type
Returns
unsigned int
See also
LANGUAGE unsigned int
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > String
          
string
          [Data Types]
          
Description
> String
          
string
          [Data Types]
          
Description
Text strings can be represented in two ways. you can use the String data type, which is part of the core as of version 0019, or you can make a string out of an array of type char and null-terminate it. This page described the latter method. For more details on the String object, which gives you more functionality at the cost of more memory, see the String object page.
Syntax
All of the following are valid declarations for strings.
char Str1[15];
char Str2[8] = {'a', 'r', 'd', 'u', 'i', 'n', 'o'};
char Str3[8] = {'a', 'r', 'd', 'u', 'i', 'n', 'o', '\0'};
char Str4[] = "arduino";
char Str4[] = "arduino";
char Str5[8] = "arduino";
char Str6[15] = "arduino";
Possibilities for declaring strings
Declare an array of chars without initializing it as in Str1
Declare an array of chars (with one extra char) and the compiler will add the required null character, as in Str2
Explicitly add the null character, Str3
Initialize with a string constant in quotation marks; the compiler will size the array to fit the string constant and a terminating null character, Str4
Initialize the array with an explicit size and string constant, Str5
Initialize the array, leaving extra space for a larger string, Str6
Null termination
Generally, strings are terminated with a null character (ASCII code 0). This allows functions (like Serial.print()) to tell where the end of a string is. Otherwise, they would continue reading subsequent bytes of memory that aren’t actually part of the string.
This means that your string needs to have space for one more character than the text you want it to contain. That is why Str2 and Str5 need to be eight characters, even though "arduino" is only seven - the last position is automatically filled with a null character. Str4 will be automatically sized to eight characters, one for the extra null. In Str3, we’ve explicitly included the null character (written '\0') ourselves.
Note that it’s possible to have a string without a final null character (e.g. if you had specified the length of Str2 as seven instead of eight). This will break most functions that use strings, so you shouldn’t do it intentionally. If you notice something behaving strangely (operating on characters not in the string), however, this could be the problem.
Single quotes or double quotes?
Strings are always defined inside double quotes ("Abc") and characters are always defined inside single quotes('A').
Wrapping long strings
You can wrap long strings like this:
char myString[] = "This is the first line"
" this is the second line"
" etcetera";
Arrays of strings
It is often convenient, when working with large amounts of text, such as a project with an LCD display, to setup an array of strings. Because strings themselves are arrays, this is actually an example of a two-dimensional array.
In the code below, the asterisk after the datatype char “char*” indicates that this is an array of “pointers”. All array names are actually pointers, so this is required to make an array of arrays. Pointers are one of the more esoteric parts of C++ for beginners to understand, but it isn’t necessary to understand pointers in detail to use them effectively here.
Example Code
Example Code
char *myStrings[] = {"This is string 1", "This is string 2", "This is string 3",
                     "This is string 4", "This is string 5", "This is string 6"
                    };
void setup() {
  Serial.begin(9600);
}
void loop() {
  for (int i = 0; i < 6; i++) {
    Serial.println(myStrings[i]);
    delay(500);
  }
}
See also
LANGUAGE PROGMEM
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Void
          
void
          [Data Types]
          
Description
The void keyword is used only in function declarations. It indicates that the function is expected to return no information to the function from which it was called.
Example Code
The code shows how to use void.
// actions are performed in the functions "setup" and "loop"
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Reference
            >  Language
            >  Variables
            >  Data types
            > Int
          
int
          [Data Types]
          
Description
Integers are your primary data-type for number storage.
Description
Integers are your primary data-type for number storage.
On the Arduino Uno (and other ATmega based boards) an int stores a 16-bit (2-byte) value. This yields a range of -32,768 to 32,767 (minimum value of -2^15 and a maximum value of (2^15) - 1).
On the Arduino Due and SAMD based boards (like MKR1000 and Zero), an int stores a 32-bit (4-byte) value. This yields a range of -2,147,483,648 to 2,147,483,647 (minimum value of -2^31 and a maximum value of (2^31) - 1).
int’s store negative numbers with a technique called (2’s complement math). The highest bit, sometimes referred to as the "sign" bit, flags the number as a negative number. The rest of the bits are inverted and 1 is added.
The Arduino takes care of dealing with negative numbers for you, so that arithmetic operations work transparently in the expected manner. There can be an unexpected complication in dealing with the bitshift right operator (>>) however.
Syntax
int var = val;
Parameters
var: variable name.
val: the value you assign to that variable.
Example Code
This code creates an integer called 'countUp', which is initially set as the number 0 (zero). The variable goes up by 1 (one) each loop, being displayed on the serial monitor.
int countUp = 0;            //creates a variable integer called 'countUp'
void setup() {
void setup() {
  Serial.begin(9600);       // use the serial port to print the number
}
void loop() {
  countUp++;                //Adds 1 to the countUp int on every loop
  Serial.println(countUp);  // prints out the current state of countUp
  delay(1000);
}
Notes and Warnings
When signed variables are made to exceed their maximum or minimum capacity they overflow. The result of an overflow is unpredictable so this should be avoided. A typical symptom of an overflow is the variable "rolling over" from its maximum capacity to its minimum or vice versa, but this is not always the case. If you want this behavior, use unsigned int.
See also
LANGUAGE Integer Constants
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Word
          
word
          [Data Types]
          
Description
A word can store an unsigned number of at least 16 bits (from 0 to 65535).
Syntax
word var = val;
Parameters
var: variable name.
val: the value to assign to that variable.
Example Code
Language
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structure
Libraries
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Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Float
          
float
          [Data Types]
          
Description
> Float
          
float
          [Data Types]
          
Description
Datatype for floating-point numbers, a number that has a decimal point. Floating-point numbers are often used to approximate analog and continuous values because they have greater resolution than integers. Floating-point numbers can be as large as 3.4028235E+38 and as low as -3.4028235E+38. They are stored as 32 bits (4 bytes) of information.
Syntax
float var = val;
Parameters
var: variable name.
val: the value you assign to that variable.
Example Code
float myfloat;
float sensorCalbrate = 1.117;
int x;
int y;
float z;
x = 1;
y = x / 2;          // y now contains 0, ints can't hold fractions
z = (float)x / 2.0; // z now contains .5 (you have to use 2.0, not 2)
Notes and Warnings
If doing math with floats, you need to add a decimal point, otherwise it will be treated as an int. See the Floating point constants page for details.
The float data type has only 6-7 decimal digits of precision. That means the total number of digits, not the number to the right of the decimal point. Unlike other platforms, where you can get more precision by using a double (e.g. up to 15 digits), on the Arduino, double is the same size as float.
Floating point numbers are not exact, and may yield strange results when compared. For example 9.0 / 0.3 may not quite equal 30.0. You should instead check that the absolute value of the difference between the numbers is less than some small number.
Conversion from floating point to integer math results in truncation:
float x = 2.9; // A float type variable
int y = x;  // 2
If, instead, you want to round off during the conversion process, you need to add 0.5:
float x = 2.9;
int y = x + 0.5;  // 3
or use the round() function:
float x = 2.9;
int y = round(x);  // 3
Floating point math is also much slower than integer math in performing calculations, so should be avoided if, for example, a loop has to run at top speed for a critical timing function. Programmers often go to some lengths to convert floating point calculations to integer math to increase speed.
See also
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Long
          
long
          [Data Types]
          
Description
Long variables are extended size variables for number storage, and store 32 bits (4 bytes), from -2,147,483,648 to 2,147,483,647.
If doing math with integers at least one of the values must be of type long, either an integer constant followed by an L or a variable of type long, forcing it to be a long. See the Integer Constants page for details.
Syntax
long var = val;
Parameters
var: variable name.
val: the value assigned to the variable.
Example Code
long speedOfLight_km_s = 300000L;  // see the Integer Constants page for explanation of the 'L'
See also
LANGUAGE Integer Constants
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Boolean
          
boolean
          [Data Types]
          
Description
boolean is a non-standard type alias for bool defined by Arduino. It’s recommended to instead use the standard type bool, which is identical.
See also
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Bool
          
bool
          [Data Types]
          
Description
A bool holds one of two values, true or false. (Each bool variable occupies one byte of memory.)
Syntax
bool var = val;
Parameters
var: variable name.
val: the value to assign to that variable.
Example Code
var: variable name.
val: the value to assign to that variable.
Example Code
This code shows how to use the bool datatype.
int LEDpin = 5;     // LED on pin 5
int switchPin = 13; // momentary switch on 13, other side connected to ground
bool running = false;
void setup() {
  pinMode(LEDpin, OUTPUT);
  pinMode(switchPin, INPUT);
  digitalWrite(switchPin, HIGH);  // turn on pullup resistor
}
void loop() {
  if (digitalRead(switchPin) == LOW) {
    // switch is pressed - pullup keeps pin high normally
    delay(100);                     // delay to debounce switch
    running = !running;             // toggle running variable
    digitalWrite(LEDpin, running);  // indicate via LED
  }
}
See also
LANGUAGE constants
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Stringobject
          
String()
          [Data Types]
          
Description
Constructs an instance of the String class. There are multiple versions that construct Strings from different data types (i.e. format them as sequences of characters), including:
a constant string of characters, in double quotes (i.e. a char array)
a constant string of characters, in double quotes (i.e. a char array)
a single constant character, in single quotes
another instance of the String object
a constant integer or long integer
a constant integer or long integer, using a specified base
an integer or long integer variable
an integer or long integer variable, using a specified base
a float or double, using a specified decimal places
Constructing a String from a number results in a string that contains the ASCII representation of that number. The default is base ten, so
String thisString = String(13);
gives you the String "13". You can use other bases, however. For example,
String thisString = String(13, HEX);
gives you the String "d", which is the hexadecimal representation of the decimal value 13. Or if you prefer binary,
String thisString = String(13, BIN);
String thisString = String(13, BIN);
gives you the String "1101", which is the binary representation of 13.
Syntax
String(val)
String(val, base)
String(val, decimalPlaces)
Parameters
val:  a variable to format as a String. Allowed data types: string, char, byte, int, long, unsigned int, unsigned long, float, double.
base: (optional) the base in which to format an integral value.
decimalPlaces: only if val is float or double. The desired decimal places.
Returns
An instance of the String class.
Example Code
All of the following are valid declarations for Strings.
String stringOne = "Hello String";                    // using a constant String
String stringOne = String('a');                       // converting a constant char into a String
String stringTwo = String("This is a string");        // converting a constant string into a String object
String stringOne = String(stringTwo + " with more");  // concatenating two strings
String stringOne = String(13);                        // using a constant integer
String stringOne = String(analogRead(0), DEC);        // using an int and a base
String stringOne = String(45, HEX);                   // using an int and a base (hexadecimal)
String stringOne = String(255, BIN);                  // using an int and a base (binary)
String stringOne = String(millis(), DEC);             // using a long and a base
String stringOne = String(5.698, 3);                  // using a float and the decimal places
Functions
LANGUAGE charAt()
LANGUAGE compareTo()
LANGUAGE concat()
LANGUAGE c_str()
LANGUAGE endsWith()
LANGUAGE equals()
LANGUAGE equalsIgnoreCase()
LANGUAGE getBytes()
LANGUAGE indexOf()
LANGUAGE lastIndexOf()
LANGUAGE length()
LANGUAGE remove()
LANGUAGE indexOf()
LANGUAGE lastIndexOf()
LANGUAGE length()
LANGUAGE remove()
LANGUAGE replace()
LANGUAGE reserve()
LANGUAGE setCharAt()
LANGUAGE startsWith()
LANGUAGE substring()
LANGUAGE toCharArray()
LANGUAGE toDouble()
LANGUAGE toInt()
LANGUAGE toFloat()
LANGUAGE toLowerCase()
LANGUAGE toUpperCase()
LANGUAGE trim()
Operators
LANGUAGE [] (element access)
LANGUAGE + (concatenation)
LANGUAGE += (append)
LANGUAGE == (comparison)
LANGUAGE > (greater than)
LANGUAGE >= (greater than or equal to)
LANGUAGE < (less than)
LANGUAGE <= (less than or equal to)
LANGUAGE != (different from)
EXAMPLE String Tutorials
See also
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Size t
          
size_t
          [Data Types]
          
Description
size_t is a data type capable of representing the size of any object in bytes. Examples of the use of size_t are the return type of sizeof() and Serial.print().
Syntax
size_t var = val;
Parameters
var: variable name.
Language
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Reference
            >  Language
            >  Variables
            >  Data types
            > Short
          
short
          [Data Types]
          
Description
A short is a 16-bit data-type.
Description
A short is a 16-bit data-type.
On all Arduinos (ATMega and ARM based) a short stores a 16-bit (2-byte) value. This yields a range of -32,768 to 32,767 (minimum value of -2^15 and a maximum value of (2^15) - 1).
Syntax
short var = val;
Parameters
var: variable name.
val: the value you assign to that variable.
Example Code
short ledPin = 13
See also
LANGUAGE Integer Constants
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Double
          
double
          [Data Types]
          
Description
Double precision floating point number. On the Uno and other ATMEGA based boards, this occupies 4 bytes. That is, the double implementation is exactly the same as the float, with no gain in precision.
Language
functions
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Libraries
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Reference
            >  Language
            >  Variables
            >  Data types
            > Unsignedchar
          
unsigned char
          [Data Types]
          
Description
An unsigned data type that occupies 1 byte of memory. Same as the byte datatype.
The unsigned char datatype encodes numbers from 0 to 255.
For consistency of Arduino programming style, the byte data type is to be preferred.
Syntax
Language
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Reference
            >  Language
            >  Variables
            >  Data types
            > Unsignedint
          
unsigned int
          [Data Types]
          
Description
> Unsignedint
          
unsigned int
          [Data Types]
          
Description
On the Uno and other ATMEGA based boards, unsigned ints (unsigned integers) are the same as ints in that they store a 2 byte value. Instead of storing negative numbers however they only store positive values, yielding a useful range of 0 to 65,535 ((2^16) - 1).
The Due stores a 4 byte (32-bit) value, ranging from 0 to 4,294,967,295 (2^32 - 1).
The difference between unsigned ints and (signed) ints, lies in the way the highest bit, sometimes referred to as the "sign" bit, is interpreted. In the Arduino int type (which is signed), if the high bit is a "1", the number is interpreted as a negative number, and the other 15 bits are interpreted with (2’s complement math).
Syntax
Syntax
unsigned int var = val;
Parameters
var: variable name.
val: the value you assign to that variable.
Example Code
unsigned int ledPin = 13;
Notes and Warnings
When unsigned variables are made to exceed their maximum capacity they "roll over" back to 0, and also the other way around:
unsigned int x;
x = 0;
x = x - 1;  // x now contains 65535 - rolls over in neg direction
x = x + 1;  // x now contains 0 - rolls over
Math with unsigned variables may produce unexpected results, even if your unsigned variable never rolls over.
The MCU applies the following rules:
The calculation is done in the scope of the destination variable. E.g. if the destination variable is signed, it will do signed math, even if both input variables are unsigned.
However with a calculation which requires an intermediate result, the scope of the intermediate result is unspecified by the code. In this case, the MCU will do unsigned math for the intermediate result, because both inputs are unsigned!
unsigned int x = 5;
unsigned int y = 10;
int result;
result = x - y; // 5 - 10 = -5, as expected
result = (x - y) / 2; // 5 - 10 in unsigned math is 65530!  65530/2 = 32765
// solution: use signed variables, or do the calculation step by step.
result = x - y; // 5 - 10 = -5, as expected
result = result / 2;  //  -5/2 = -2 (only integer math, decimal places are dropped)
Why use unsigned variables at all?
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Reference
            >  Language
            >  Variables
            >  Data types
            > Char
          
char
          [Data Types]
          
Description
A data type used to store a character value. Character literals are written in single quotes, like this: 'A' (for multiple characters - strings - use double quotes: "ABC").
Characters are stored as numbers however. You can see the specific encoding in the ASCII chart. This means that it is possible to do arithmetic on characters, in which the ASCII value of the character is used (e.g. 'A' + 1 has the value 66, since the ASCII value of the capital letter A is 65). See Serial.println reference for more on how characters are translated to numbers.
The size of the char datatype is at least 8 bits. It’s recommended to only use char for storing characters. For an unsigned, one-byte (8 bit) data type, use the byte data type.
Syntax
char var = val;
Parameters
var: variable name.
val: the value to assign to that variable.
Example Code
char myChar = 'A';
char myChar = 65; // both are equivalent
See also
LANGUAGE Serial.println
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Byte
          
byte
          [Data Types]
          
Description
A byte stores an 8-bit unsigned number, from 0 to 255.
Syntax
byte var = val;
Parameters
var: variable name.
val: the value to assign to that variable.
See also
LANGUAGE byte()
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Array
          
array
          [Data Types]
          
Description
An array is a collection of variables that are accessed with an index number. Arrays in the C++ programming language Arduino sketches are written in can be complicated, but using simple arrays is relatively straightforward.
Creating (Declaring) an Array
Creating (Declaring) an Array
All of the methods below are valid ways to create (declare) an array.
  int myInts[6];
  int myPins[] = {2, 4, 8, 3, 6};
  int mySensVals[5] = {2, 4, -8, 3, 2};
  char message[6] = "hello";
You can declare an array without initializing it as in myInts.
In myPins we declare an array without explicitly choosing a size. The compiler counts the elements and creates an array of the appropriate size.
Finally you can both initialize and size your array, as in mySensVals. Note that when declaring an array of type char, one more element than your initialization is required, to hold the required null character.
Accessing an Array
Accessing an Array
Arrays are zero indexed, that is, referring to the array initialization above, the first element of the array is at index 0, hence
mySensVals[0] == 2, mySensVals[1] == 4, and so forth.
It also means that in an array with ten elements, index nine is the last element. Hence:
int myArray[10]={9, 3, 2, 4, 3, 2, 7, 8, 9, 11};
// myArray[9]    contains 11
// myArray[10]   is invalid and contains random information (other memory address)
// myArray[10]   is invalid and contains random information (other memory address)
For this reason you should be careful in accessing arrays. Accessing past the end of an array (using an index number greater than your declared array size - 1) is reading from memory that is in use for other purposes. Reading from these locations is probably not going to do much except yield invalid data. Writing to random memory locations is definitely a bad idea and can often lead to unhappy results such as crashes or program malfunction. This can also be a difficult bug to track down.
Unlike BASIC or JAVA, the C++ compiler does no checking to see if array access is within legal bounds of the array size that you have declared.
To assign a value to an array:
mySensVals[0] = 10;
To retrieve a value from an array:
x = mySensVals[4];
Arrays and FOR Loops
x = mySensVals[4];
Arrays and FOR Loops
Arrays are often manipulated inside for loops, where the loop counter is used as the index for each array element. For example, to print the elements of an array over the serial port, you could do something like this:
for (byte i = 0; i < 5; i = i + 1) {
  Serial.println(myPins[i]);
}
Example Code
For a complete program that demonstrates the use of arrays, see the (How to Use Arrays example) from the (Built-in Examples).
See also
LANGUAGE PROGMEM
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Data types
            > Unsignedlong
          
unsigned long
          [Data Types]
          
Description
> Unsignedlong
          
unsigned long
          [Data Types]
          
Description
Unsigned long variables are extended size variables for number storage, and store 32 bits (4 bytes). Unlike standard longs unsigned longs won’t store negative numbers, making their range from 0 to 4,294,967,295 (2^32 - 1).
Syntax
unsigned long var = val;
Parameters
var: variable name.
val: the value you assign to that variable.
Example Code
unsigned long time;
void setup() {
  Serial.begin(9600);
}
void loop() {
  Serial.print("Time: ");
  time = millis();
  //prints time since program started
  Serial.println(time);
  // wait a second so as not to send massive amounts of data
  delay(1000);
}
See also
LANGUAGE Integer Constants
Language
functions
variables
structure
Libraries
IoT Cloud API
Glossary
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Reference
            >  Language
            >  Variables
            >  Utilities
            > Progmem
          
PROGMEM
          [Utilities]
          
Description
Store data in flash (program) memory instead of SRAM. There’s a description of the various types of memory available on an Arduino board.
The PROGMEM keyword is a variable modifier, it should be used only with the datatypes defined in pgmspace.h. It tells the compiler "put this information into flash memory", instead of into SRAM, where it would normally go.
PROGMEM is part of the pgmspace.h library. It is included automatically in modern versions of the IDE. However, if you are using an IDE version below 1.0 (2011), you’ll first need to include the library at the top of your sketch, like this:
#include <avr/pgmspace.h>
While PROGMEM could be used on a single variable, it is really only worth the fuss if you have a larger block of data that needs to be stored, which is usually easiest in an array, (or another C++ data structure beyond our present discussion).
Using PROGMEM is also a two-step procedure. After getting the data into Flash memory, it requires special methods (functions), also defined in the pgmspace.h library, to read the data from program memory back into SRAM, so we can do something useful with it.
Syntax
const dataType variableName[] PROGMEM = {data0, data1, data3…​};
Note that because PROGMEM is a variable modifier, there is no hard and fast rule about where it should go, so the Arduino compiler accepts all of the definitions below, which are also synonymous. However, experiments have indicated that, in various versions of Arduino (having to do with GCC version), PROGMEM may work in one location and not in another. The "string table" example below has been tested to work with Arduino 13. Earlier versions of the IDE may work better if PROGMEM is included after the variable name.
const dataType variableName[] PROGMEM = {};  // use this form
const dataType variableName[] PROGMEM = {};  // use this form
const PROGMEM dataType variableName[] = {};  // or this one
const dataType PROGMEM variableName[] = {};  // not this one
Parameters
dataType: Allowed data types: any variable type.
variableName: the name for your array of data.
Example Code
The following code fragments illustrate how to read and write unsigned chars (bytes) and ints (2 bytes) to PROGMEM.
// save some unsigned ints
const PROGMEM uint16_t charSet[] = { 65000, 32796, 16843, 10, 11234};
// save some chars
const char signMessage[] PROGMEM = {"I AM PREDATOR,  UNSEEN COMBATANT. CREATED BY THE UNITED STATES DEPART"};
unsigned int displayInt;
char myChar;
void setup() {
  Serial.begin(9600);
char myChar;
void setup() {
  Serial.begin(9600);
  while (!Serial);  // wait for serial port to connect. Needed for native USB
  // put your setup code here, to run once:
  // read back a 2-byte int
  for (byte k = 0; k < 5; k++) {
    displayInt = pgm_read_word_near(charSet + k);
    Serial.println(displayInt);
  }
  Serial.println();
  // read back a char
  for (byte k = 0; k < strlen_P(signMessage); k++) {
    myChar = pgm_read_byte_near(signMessage + k);
    Serial.print(myChar);
  }
  Serial.println();
}
void loop() {
  // put your main code here, to run repeatedly:
}
Arrays of strings
// put your main code here, to run repeatedly:
}
Arrays of strings
It is often convenient when working with large amounts of text, such as a project with an LCD, to setup an array of strings. Because strings themselves are arrays, this is actually an example of a two-dimensional array.
These tend to be large structures so putting them into program memory is often desirable. The code below illustrates the idea.
/*
  PROGMEM string demo
  How to store a table of strings in program memory (flash),
  and retrieve them.
  Information summarized from:
  http://www.nongnu.org/avr-libc/user-manual/pgmspace.html
  Setting up a table (array) of strings in program memory is slightly complicated, but
  here is a good template to follow.
  Setting up the strings is a two-step process. First, define the strings.
*/
#include <avr/pgmspace.h>
*/
#include <avr/pgmspace.h>
const char string_0[] PROGMEM = "String 0"; // "String 0" etc are strings to store - change to suit.
const char string_1[] PROGMEM = "String 1";
const char string_2[] PROGMEM = "String 2";
const char string_3[] PROGMEM = "String 3";
const char string_4[] PROGMEM = "String 4";
const char string_5[] PROGMEM = "String 5";
// Then set up a table to refer to your strings.
const char *const string_table[] PROGMEM = {string_0, string_1, string_2, string_3, string_4, string_5};
char buffer[30];  // make sure this is large enough for the largest string it must hold
void setup() {
  Serial.begin(9600);
void setup() {
  Serial.begin(9600);
  while (!Serial);  // wait for serial port to connect. Needed for native USB
  Serial.println("OK");
}
void loop() {
  /* Using the string table in program memory requires the use of special functions to retrieve the data.
     The strcpy_P function copies a string from program space to a string in RAM ("buffer").
     Make sure your receiving string in RAM is large enough to hold whatever
     you are retrieving from program space. */
  for (int i = 0; i < 6; i++) {
    strcpy_P(buffer, (char *)pgm_read_word(&(string_table[i])));  // Necessary casts and dereferencing, just copy.
    Serial.println(buffer);
    delay(500);
  }
}
Notes and Warnings