Arrays and Pointers – Understanding Their Relationship

UpdatedMarch 9, 2026

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C Programming

Part 21 of 40

From today, I will be starting lessons on C programming in my ALX Software Engineering class and I look forward to sharing with you everything I learn through this series.

Up next

Strings in C – Arrays of Characters

In the previous lessons, you learned about: Arrays Pointers How arrays and pointers are related Now we will apply that knowledge to something very common in programming: strings. In C, strings ar

1. The Most Important Idea

When you declare an array:

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

The name a represents:

The address of the first element.

So:

a == &a[0]

That is extremely important.

The array name behaves like a pointer to its first element.

2. Visualizing Memory

Suppose memory looks like this:

Address   Value
1000      10
1004      20
1008      30
1012      40
1016      50

If a stores address 1000, then:

a      → 1000
a + 1  → 1004
a + 2  → 1008

Each time you add 1, it moves by the size of an int.

That is pointer arithmetic.

3. Pointer Arithmetic

Let’s look at this code:

#include <stdio.h>

int main() {
    int a[3] = {10, 20, 30};

    printf("%d\n", *a);
    printf("%d\n", *(a + 1));
    printf("%d\n", *(a + 2));

    return 0;
}

Output:

10
20
30

Why?

Because:

*a       == a[0]
*(a+1)   == a[1]
*(a+2)   == a[2]

So this means:

a[i] == *(a + i)

They are equivalent.

4. Why This Works

When you write:

a[i]

C internally translates it to:

*(a + i)

So indexing is just pointer arithmetic combined with dereferencing.

This is not magic.

It is simple math with memory addresses.

5. Using a Pointer to Traverse an Array

You can also use a pointer variable:

#include <stdio.h>

int main() {
    int a[3] = {10, 20, 30};
    int *p = a;

    for (int i = 0; i < 3; i++) {
        printf("%d\n", *(p + i));
    }

    return 0;
}

Here:

p stores the address of a[0]
p + 1 moves to the next element
*(p + i) retrieves the value

6. Are Arrays and Pointers the Same?

They behave similarly.

But they are NOT the same.

Important differences:

1. Arrays have fixed size

int a[5];

You cannot change the size of a.

2. Array name cannot be reassigned

This is illegal:

a = some_other_address;   // Error

Array names are constant addresses.

3. Pointers can be reassigned

int x = 10;
int y = 20;

int *p = &x;
p = &y;   // Allowed

Pointers are flexible.

Arrays are fixed.

7. Why This Matters

Understanding arrays and pointers helps you:

Work with strings
Pass arrays to functions
Manage memory
Understand how C really works

If you skip this understanding, advanced topics will feel confusing.

8. Common Mistakes

❌ Confusing pointer arithmetic

When you write:

p + 1

It does NOT move by 1 byte.

It moves by:

sizeof(data_type)

If p is int*, it moves 4 bytes (usually).

❌ Forgetting array bounds

Even with pointer arithmetic, you must stay inside the array.

C will not protect you.

9. Practice Exercises

Create an array of 4 integers and print them using:
- indexing (a[i])
- pointer arithmetic (*(a + i))
Assign a pointer to an array and use it to modify elements.
Draw memory layout for:
```
int a[3] = {5, 6, 7};
```
Explain why a[2] equals *(a + 2).

Final Thoughts

Today you learned something powerful:

Array names are addresses.
Indexing is pointer arithmetic.
a[i] is the same as *(a + i).
Arrays and pointers are related but not identical.

This understanding makes C much clearer.

In the next lesson, we will move to strings — which are just arrays of characters.

And everything you learned today will make that lesson easier.

Arrays and Pointers – Understanding Their Relationship

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1. The Most Important Idea

2. Visualizing Memory

3. Pointer Arithmetic

4. Why This Works

5. Using a Pointer to Traverse an Array

6. Are Arrays and Pointers the Same?

1. Arrays have fixed size

2. Array name cannot be reassigned

3. Pointers can be reassigned

7. Why This Matters

8. Common Mistakes

❌ Confusing pointer arithmetic

❌ Forgetting array bounds

9. Practice Exercises

Final Thoughts

Command Palette

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C Programming

Strings in C – Arrays of Characters

More from this blog

1. The Most Important Idea

2. Visualizing Memory

3. Pointer Arithmetic

4. Why This Works

5. Using a Pointer to Traverse an Array

6. Are Arrays and Pointers the Same?

1. Arrays have fixed size

2. Array name cannot be reassigned

3. Pointers can be reassigned

7. Why This Matters

8. Common Mistakes

❌ Confusing pointer arithmetic

❌ Forgetting array bounds

9. Practice Exercises

Final Thoughts