Pointers & Arrays

⚙️ C Language 🟢 Lesson 12 of 20 📅 2026 Edition

Arrays and pointers are deeply connected in C — in fact, an array's name is really just a pointer to its first element in disguise. Understanding this relationship unlocks a much deeper understanding of how C actually works.

1An Array Name Is a Pointer

C Language ▶ Run Code

int numbers[5] = {10, 20, 30, 40, 50};

printf("%p\n", numbers);     // address of the first element
printf("%p\n", &numbers[0]); // the exact same address
printf("%d\n", *numbers);    // 10 - dereferencing gives the first value

This is why, as mentioned in Lesson 4, you never write &numbers when passing an array to scanf() — the array name already behaves like an address.

2Pointer Arithmetic

You can move a pointer forward through an array by adding to it — and C automatically scales the math by the size of the data type:

C Language ▶ Run Code

int numbers[5] = {10, 20, 30, 40, 50};
int *ptr = numbers;

printf("%d\n", *ptr);       // 10
printf("%d\n", *(ptr + 1)); // 20 - moves forward one INT, not one byte
printf("%d\n", *(ptr + 2)); // 30

3Looping Through an Array Using a Pointer

C Language ▶ Run Code

int numbers[5] = {10, 20, 30, 40, 50};
int *ptr = numbers;

for (int i = 0; i < 5; i++) {
    printf("%d\n", *(ptr + i));
}

This produces exactly the same output as numbers[i] — in fact, numbers[i] is literally just shorthand the compiler translates into *(numbers + i) behind the scenes.

4Passing Arrays to Functions

C Language ▶ Run Code

void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int numbers[5] = {1, 2, 3, 4, 5};
    printArray(numbers, 5);   // no & needed, and size must be passed separately
    return 0;
}

Unlike single variables, arrays are effectively always passed by reference in C — the function receives the actual array's address, not a copy, so changes made inside the function do affect the original array.

⚠️ Common Mistake: Forgetting to Pass the Array Size to a Function

Unlike a Python list, a C array passed into a function loses all information about its own size — the function only receives a pointer to the first element. If you forget to pass the size as a separate parameter, the function has no way to know when the array ends, and will happily read past its end into unrelated memory.

💻 Try It Yourself

Write a function that takes an array and its size, and returns the largest value found in the array.

C Language ▶ Run Code

#include <stdio.h>

int findMax(int arr[], int size) {
    int max = arr[0];
    for (int i = 1; i < size; i++) {
        if (arr[i] > max) {
            max = arr[i];
        }
    }
    return max;
}

int main() {
    int numbers[6] = {23, 67, 12, 89, 45, 33};
    printf("Max: %d\n", findMax(numbers, 6));
    return 0;
}

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