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1. Core C Basics for Embedded Systems

Your Foundation for Embedded Programming

Topics Covered:

  • Variables & Data Types
  • Operators & Control Flow
  • Functions
  • Arrays & Strings
  • Basic Input/Output
  • Practice Problems

1.1 Variables & Data Types

What is a Variable?

A variable is a named location in memory that stores data. Think of it as a labeled box where you can put values and retrieve them later.

Note: In embedded systems, understanding how much memory each data type uses is CRITICAL because microcontrollers have limited RAM.

Common Data Types in C

Data Type Size (Typical) Range Use Case
char 1 byte -128 to 127 Single characters, small integers
unsigned char 1 byte 0 to 255 Sensor readings, register values
int (16-bit) 2 bytes -32,768 to 32,767 Counters, calculations
unsigned int 2 bytes 0 to 65,535 (16-bit) Always positive values
long 4 bytes -2,147,483,648 to 2,147,483,647 Large numbers, timestamps
float 4 bytes ±3.4e±38 (~6–7 digits precision) Decimal numbers (avoid in embedded!)

Example Code:

// Declaring variables
int sensorValue = 0; // 16 or 32-bit integer
unsigned char ledState = 1; // 8-bit (0-255)
float temperature = 25.5; // Floating point
char deviceStatus = 'A'; // Single character

// Why size matters in embedded:
unsigned char counter = 0; // Uses only 1 byte of RAM
int bigCounter = 0; // Uses 2 or 4 bytes of RAM

1.2. Operators & Control Flow

Arithmetic Operators

Used for mathematical calculations: + (add), - (subtract), * (multiply), / (divide), % (modulus/remainder)

int a = 10, b = 3;
int sum = a + b; // 13
int diff = a - b; // 7
int product = a * b; // 30
int quotient = a / b; // 3 (integer division!)
int remainder = a % b; // 1

Comparison Operators

Compare values and return true (1) or false (0):

==      (equal),
!=      (not equal),
>       (greater),
<       (less),
>=, <=

Logical Operators

Combine multiple conditions: && (AND), || (OR),! (NOT)

int temperature = 75;
int humidity = 60;

// AND operator - both conditions must be true
if (temperature > 70 && humidity > 50) {
    printf("Hot and humid!\n");
}

Control Flow: if/else

Makes decisions in your program based on conditions.

int temperature = 75;
if (temperature > 80) {
    // Turn on cooling fan
    fanState = 1;
} else if (temperature < 60) {
    // Turn on heater
    heaterState = 1;
} else {
    // Temperature is fine
    fanState = 0;
    heaterState = 0;
}

Loops: for and while

Repeat code multiple times. Essential for embedded systems!

// for loop - when you know how many times to repeat
for (int i = 0; i < 10; i++) {
    printf("%d ", i); // Prints: 0 1 2 3 4 5 6 7 8 9
}

// while loop - repeat while condition is true
int count = 0;
while (count < 5) {
    printf("Count: %d\n", count);
    count++;
}

Embedded Tip: In embedded systems, you'll often use infinite loops: while(1) { } to keep the microcontroller running continuously!

1.3. Functions

What are Functions?

Functions are reusable blocks of code that perform a specific task. They help you organize code and avoid repetition.

Function Structure

return_type function_name(parameters) {
    // code to execute
    return value; // optional
}

Example: Simple Functions

// Function that returns sum of two numbers
int add(int a, int b) {
    return a + b;
}

// Function that doesn't return anything (void)
void blinkLED(int times) {
    for (int i = 0; i < times; i++) {
        // Turn LED on
        // Delay
        // Turn LED off
        // Delay
    }
}

// Using the functions
int main() {
    int result = add(5, 3); // result = 8
    blinkLED(5); // Blink LED 5 times
    return 0;
}

Why Functions Matter in Embedded: Real embedded projects have functions like readSensor(), updateDisplay(), checkButton() - breaking complex tasks into simple, manageable pieces.

1.4. Arrays & Strings

What is an Array?

An array is a collection of elements of the same type stored in consecutive memory locations. Think of it as a row of boxes, each holding a value.

Declaring and Using Arrays

// Declare an array of 5 integers
int sensorReadings[5];

// Initialize array with values
int ledPins[4] = {2, 3, 4, 5};

// Access array elements (index starts at 0!)
sensorReadings[0] = 100; // First element
sensorReadings[1] = 105; // Second element
sensorReadings[4] = 120; // Fifth element

// Loop through array
for (int i = 0; i < 5; i++) {
    printf("%d ", sensorReadings[i]);
}

Strings in C

In C, strings are arrays of characters ending with a null terminator ('\0'). This is different from other languages!

// Declaring strings
char deviceName[] = "Arduino"; // Automatically adds \
char message[20] = "Hello World"; // Reserve 20 chars

// Character array vs string
char name[6] = {'C', 'l', 'a', 'u', 'd', '\0'}; // Must add \

// Common string operations (need string.h)
#include <string.h>
char str1[50] = "Hello";
char str2[50] = "World";
strcat(str1, str2); // Concatenate: str1 becomes "HelloWorld"
int len = strlen(str1); // Get length: 10
strcpy(str1, "New"); // Copy: str1 becomes "New"

Important: In embedded systems, you'll often use character arrays to store sensor data, messages for displays, or communication buffers.

1.5. Basic Input/Output

Console Output: printf()

printf() is used to print formatted output to the console. Essential for debugging embedded systems!

#include <stdio.h>

int temperature = 25;
float voltage = 3.3;
char status = 'A';

// Format specifiers:
printf("Temperature: %d°C\n", temperature); // %d for integers
printf("Voltage: %.2f V\n", voltage); // %f for floats (.2 = 2 decimals)
printf("Status: %c\n", status); // %c for characters
printf("Hex value: 0x%X\n", 255); // %X for hexadecimal

// Multiple values:
printf("Temp: %d, Voltage: %.1f\n", temperature, voltage);

Console Input: scanf()

scanf() reads formatted input from the console.

int age;
char name[50];

printf("Enter your age: ");
scanf("%d", &age); // Note the & symbol!

printf("Enter your name: ");
scanf("%s", name); // No & for arrays

printf("Hello %s, you are %d years old!\n", name, age);

Common Format Specifiers

Specifier Data Type Example
%d or %i int printf("%d", 42);
%u unsigned int printf("%u", 255);
%f float/double printf("%.2f", 3.14);
%c char printf("%c", 'A');
%s string printf("%s", "Hello");
%x or %X hexadecimal printf("0x%X", 255);
%p pointer printf("%p", &var);

1.6. Practice Problems

Here are some hands-on exercises to solidify your understanding. Try to solve these without looking at solutions first!

Problem 1: Temperature Converter

Write a program that converts temperature from Celsius to Fahrenheit using the formula: F = (C × 9/5) + 32

// Your code here: // 1. Declare a float variable for celsius // 2. Use scanf to get input // 3. Calculate fahrenheit // 4. Print the result

Problem 2: Even or Odd Checker

Write a program that takes a number and prints whether it's even or odd. (Hint: Use the modulus operator %)

Problem 3: Sum Calculator with Loop

Write a program that takes a number N and calculates the sum of all numbers from 1 to N using a for loop. Example: If N = 5, sum = 1+2+3+4+5 = 15

Problem 4: Array Average

Create an array of 5 sensor readings. Write a function that calculates and returns the average value.

Problem 5: LED Blink Function

Write a function void blinkPattern(int count, int delayMs) that simulates blinking an LED. Use printf to show LED ON/OFF states.

Problem 5: Write a program that

  • Takes 5 temperature readings into an array
  • Calculates the average temperature
  • If average > 75°F, print "COOLING NEEDED"
  • If average < 65°F, print "HEATING NEEDED"
  • Otherwise, print "TEMPERATURE OK"