Every Arduino program, known as a sketch, is built upon a foundation of core programming concepts derived from C/C++. Mastering the fundamental building blocks—program structure, data types, variables, and operators—is essential for writing functional and efficient code for any project, from the simplest to the most complex.

2.1 Program Structure: and

An Arduino program is referred to as a sketch. Every sketch is built upon two mandatory functions that form its core structure: setup() and loop().

The setup() function is called exactly once when a sketch starts. It runs after each power-up or reset of the Arduino board. Its primary purpose is to initialize settings that are required for the program to run, such as:

• Initializing variables.
• Setting pin modes (INPUT or OUTPUT).
• Starting communication libraries (e.g., Serial.begin()).

After the setup() function completes, the loop() function begins. As its name suggests, this function runs consecutively and repeatedly, allowing your program to change, respond, and actively control the Arduino board. The code inside loop() is the main body of your program, where you will read sensor data, control actuators, and perform the primary tasks of your project.

2.2 Data Types

Data types define the nature of variables, dictating how much memory they occupy and how the bit patterns stored within that memory are interpreted. Selecting the correct data type is crucial for memory efficiency and program correctness.

2.3 Variables and Scope

Variable scope defines the region of a program where a variable can be accessed. A variable can be declared in three places, which determines its scope.

• Local Variables Variables declared inside a function or a block of code (e.g., inside a for loop) are considered local. They are only accessible within that specific function or block. Once the function or block is exited, the local variable is destroyed and its memory is reclaimed.
• Formal Parameters These are variables used in the definition of a function’s parameters. They are treated as local variables within that function.
• Global Variables Global variables are defined outside of all functions, typically at the top of the program. They are accessible by any function throughout the entire program and hold their value for the program’s lifetime. They are useful for sharing data between different parts of your sketch, such as between the loop() function and an interrupt service routine.

2.4 Operators

An operator is a symbol that instructs the compiler to perform a specific mathematical, relational, or logical function.

Arithmetic Operators

Comparison Operators

Boolean Operators

Bitwise Operators

Compound Operators

With these fundamental building blocks understood, the next step is to learn how to control the order in which they are executed.