Analog Data — Toolchain Setup Guide

In Python or JavaScript, lists and strings are highly flexible, built-in objects that manage their own memory. In C, arrays and strings are just raw, consecutive blocks of memory.

Arrays

An array is a collection of variables of the same type stored right next to each other in memory.

1#include <stdio.h>
2
3int main() {
4    // Array definition
5    int readings[5] = {100, 200, 300, 400, 500};
6    
7    // Accessing (0-indexed)
8    int first = readings[0];  // 100
9    
10    // Modifying
11    readings[1] = 250;
12    
13    printf("First reading: %d\n", first);
14
15    return 0;
16}

Buffer Overflows

C does not check array bounds. If you have an array of 5 items, and you try to write to readings[10] = 500;, C will happily overwrite whatever data happens to be living in that memory location. You must keep track of array sizes yourself.

Strings in C

C does not have a "String" type.

In C, a string is simply an Array of Characters, with a very specific rule: The last character in the array must be the "Null Terminator" (\0).

The Null Terminator

The Null Terminator is a byte with the value 0. It tells functions like printf where the string ends. Without it, printf would keep reading and printing random memory until it crashed.

1#include <stdio.h>
2
3int main() {
4    // The compiler automatically adds the '\0' at the end for you
5    char name[] = "ESP32";    
6    
7    // The array "name" is actually {'E', 'S', 'P', '3', '2', '\0'} 
8    // It takes up 6 bytes of memory, not 5!
9    
10    printf("Device: %s\n", name);
11
12    return 0;
13}

String Manipulation Functions

Because strings are just arrays, you cannot use the == operator to compare them, nor the + operator to join them. You must use functions from the <string.h> library.

1#include <stdio.h>
2#include <string.h>
3
4int main() {
5    char name[] = "ESP32";
6    
7    // 1. Get length (does NOT count the \0)
8    int len = strlen(name);              // len = 5
9    
10    // 2. Compare strings (returns 0 if they are exactly equal)
11    int cmp = strcmp(name, "ESP32");     // cmp = 0
12    
13    // 3. Find substring (returns a pointer to the start of "SP32")
14    char *found = strstr(name, "SP");    
15
16    if (cmp == 0) {
17        printf("Length of %s is %d\n", name, len);
18    }
19
20    return 0;
21}