Understanding Arduino Program Structure: A Comprehensive Guide

We open the Arduino IDE to create a new Arduino program. The newly created Arduino program is always named “sketch”.

void setup() {  // put your setup code here, to run once:
}

When the program starts, the setup() function will be called first. This function can be used to initialize variables, pin modes, enable libraries, etc.

The setup() function will only start once after the board is powered on or reset.

void loop() {  // put your main code here, to run repeatedly:
}

After the program starts and runs the setup() function, it will continuously execute the content of the loop() function. The loop() function can be executed continuously and precisely, and it is the essence of the Arduino program.

At this point, some students may wonder: “Since Arduino is edited in C/C++, why isn’t it entering the main function?” Now I will analyze this for everyone.

In Arduino development, there is no main entry function like traditional C/C++ programs. In fact, the main function exists in the Arduino core library and is still the entry point of the program. The main.cpp file can be seen in the Arduino core library, and its content is as follows:

#include <Arduino.h>
// Declared weak in Arduino.h to allow user redefinitions.
int atexit(void (* /*func*/ )()) { return 0; }
// Weak empty variant initialization function.
// May be redefined by variant files.
void initVariant() __attribute__((weak));
void initVariant() { }
void setupUSB() __attribute__((weak));
void setupUSB() { }
int main(void){        init();
        initVariant();
#if defined(USBCON)        USBDevice.attach();#endif
        setup();
        for (;;) {                loop();                if (serialEventRun) serialEventRun();        }
        return 0;}

• In Arduino, the declaration of variables

Example: int a = 0;

The declaration of a variable is in the format: type variableName = value;.

Note: The first letter of the variable name cannot be a digit.

The scope of a variable is called its scope, which is related to where the variable is declared. It can generally be divided into the following two types:

1. Global variables: Add extern before the type to declare it as a global variable, which can be used throughout the program.

1. Local variables: If a variable is defined within braces, it is a local variable, and its scope is limited to within those braces.

• In Arduino, the declaration of constants

Example: const int a = 0;

The declaration of a constant is in the format: const type variableName = value;.

Note: Once we declare a constant, we cannot assign a value to it again.

In Arduino, we can also define constants using the macro definition #define.

I prefer to use #define for definitions.

In Arduino, a string is of char type. A string is an array of char variables. A string is a special array that has an extra element at the end, which is always set to ‘\0’ (zero). This is called an “null-terminated string”.

void setup() {   char str[6];         // Create a char string of size 6   Serial.begin(9600);  // Open the serial port at 9600 baud   str[0] = 'H';    str[1] = 'e';   str[2] = 'l';   str[3] = 'l';   str[4] = 'o';        // Although we haven't assigned a null-terminated string to the array, the last element will default to a \0   Serial.println(str); // Print to the serial monitor   }

Hello

void setup() {   char str[] = "Hello";   Serial.begin(9600);   Serial.println(str);}

Output Example:

Hello

Since we can assign values, we can also modify the corresponding characters

Example:

void setup() {   char str[] = "Hello"; // create a string   Serial.begin(9600);   Serial.println(str);   str[0] = 'n';   str[1] = 'i';    str[2] = 'h';   str[3] = 'a';   str[4] = '0';   Serial.println(str);}

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