Lesson 06 of 20

6 mins read

Contiguous Arrays & Multi-Dimensional Matrices

In Plain English

An array in C is a sequence of elements stored in unbroken contiguous memory addresses. Element access arr[i] computes instantly via base_address + (i * sizeof(type)). Calculate array length using sizeof(arr) / sizeof(arr[0]) at declaration scope.

The Mental Model

"An array is a row of contiguous lockers in a gym: once you know locker #0 is at address 1000 and each locker is 4 feet wide, locker #3 is guaranteed to be at address 1012."

Deep Dive: How It Works

Contiguous Storage: Elements are laid out side-by-side in linear memory without gaps.

Sizeof Calculation: sizeof(scores) / sizeof(scores[0]) computes total element count.

Row-Major 2D Matrices: 2D arrays are stored row-by-row in linear RAM.

Syntax Blueprint

int scores[4] = {88, 92, 79, 95};
size_t count = sizeof(scores) / sizeof(scores[0]);

Declare fixed-size array and calculate element count using compile-time sizeof.

Core Rules to Remember

Zero Overhead: No hidden length fields or object wrapper overhead.

No Bounds Checking: Accessing out-of-bounds indices corrupts adjacent memory silently.

Array Decay: Arrays decay into raw pointers when passed to functions.

Common Beginner Traps & How to Fix Them

Mistake:Using sizeof(arr) / sizeof(arr[0]) inside a function where arr was passed as a parameter.

Why it happens: In functions, arrays decay to pointers, so sizeof(arr) returns the pointer size (8 bytes), not the full array.

How to fix: Always pass the array length as an explicit size_t length parameter to functions.

Pro Tip: Always track array capacities explicitly to guard against buffer overruns.

Live Interactive Example

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Average Score from Contiguous Array

C11 / GCC 9.2

Output Console

Click "Run Code" to view the rendered output.

How it works: Loop sums all 4 scores (354) and divides by 4.0 yielding 88.5.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Calculate Array Size with sizeof

Print "Total Elements: %zu\n" calculated using the sizeof idiom: sizeof(scores) / sizeof(scores[0]).

Sandbox Output

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