01_basic_c_array.md

01 — Basic C array (T a[N])

Goal

Learn how to declare a C array, fill it, print it, and sum its elements, reinforcing the idea of bounds.

Concepts

• C array: int a[5]; is a contiguous block of 5 ints.
• Valid indices: 0 to N-1.
• std::size(a): gets the number of elements of a “real” array (C++17+).
• Out-of-bounds access (e.g., a[10]) causes UB (undefined behavior).

Code explained (step by step)

File: 01_basic_c_array.cpp

1. Declare int a[5];.
2. Fill it with a for loop, using std::size(a) to avoid hardcoding the size.
3. Print each element with std::cout.
4. Compute the sum with another for loop.

Common mistakes

• Using i <= N instead of i < N (a classic off-by-one).
• Thinking a[5] is the “5th element” (the last one is a[4]).
• Mixing int with std::size_t and getting signed/unsigned comparison warnings.

Exercises

1. Change the fill to a[i] = i*i and see the new sum.
2. Compute the average of the elements (use double).
3. Find the largest and smallest element (without using algorithms yet).

How to build and run

g++ -std=c++20 -O2 -Wall -Wextra -pedantic -g 01_basic_c_array.cpp -o app
./app