#arraysinc

“Understand arrays in C programming step by step with examples, interview tips, and guidance from Seed Infotech.”

When We Are in a Classroom  the teacher calls out roll numbers: 1, 2, 3… and each student answers from their fixed seat. No chaos, no searching — every student has a number, and every number points to the right student.

That’s exactly how Arrays in C Programming work. They store values in continuous memory slots, each identified by an index. This makes finding values instant.

But here’s the catch:

What if you need more seats (memory)?

What if students (values) shift around?

That’s where understanding arrays and their limits becomes essential.

That’s where understanding arrays and their limits becomes essential. Whether you’re a student, a beginner, or preparing for coding interviews, mastering arrays is a must. Interviewers love testing them because arrays reveal how well you understand data organization and access — something students at Seed Infotech learn through hands-on coding and real-world examples.

What You’ll Learn in This Guide

What arrays in C programming are and why they matter

How arrays are stored in memory

1D, 2D, and multi-dimensional arrays with examples

Arrays vs pointers vs linked lists

Dynamic arrays with malloc & realloc

Common mistakes and pro tips

4 interview-style problems with code

By the end, you’ll not just “know” arrays — you’ll be ready to apply them in real programs and ace interviews.

How Arrays in C Programming are Stored in Memory

Arrays occupy continuous memory blocks.

Access is fast:

arr[i] = base_address + i * sizeof(type)

Array name points to the first element (like a pointer).

Example:

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

printf("%d\n", a[1]);      // 20

printf("%d\n", *(a + 1));  // 20 (pointer arithmetic)

Memory diagram:

Index:   0    1    2

Value: [10] [20] [30]

Addr:  0x100 0x104 0x108

Pro Tip: Always sketch memory layouts when practicing. It builds intuition and prevents mistakes.

Quick Task (2 min): Declare an array of 4 integers and print the address of each element.

Declaring & Initializing Arrays in C Programming

int marks[5];                         // declaration only

int marks[5] = {90, 85, 78, 92, 88};  // full initialization

int marks[5] = {90, 85};              // partial (rest = 0)

✅ Always initialize arrays. Otherwise, C language fills them with garbage values.

Types of Arrays in C Programming

1. One-Dimensional (1D) Array

A straight list of values.

int rollNo[5] = {1, 2, 3, 4, 5};

2. Two-Dimensional (2D) Array

A table-like structure.

int matrix[2][3] = {

   {1, 2, 3},

   {4, 5, 6}

};

3. Multi-Dimensional Array

A cube of data.

int cube[2][2][2];

Try This (5 min): Write a program to store marks of 3 students in 3 subjects using a 2D array.

Arrays vs Pointers

Array name = pointer to first element.

Arrays = fixed size.

Pointers = flexible, can point anywhere.

Use malloc() / realloc() for flexible arrays.

Example:

int a[3] = {1, 2, 3};

int *p = a;        // p points to a[0]

printf("%d\n", *(p+2)); // 3 ⚠️ Reminder: Arrays can’t be reassigned. Pointers can.

Arrays vs Linked Lists

Arrays → Fast access (O(1)), but fixed size.

Linked Lists → Flexible size, but slower access (O(n)).

Dynamic Arrays → Flexible with realloc, but reallocation may copy memory.

Interview Question: “When would you prefer arrays over linked lists?”

Dynamic Arrays in C Programming with malloc/realloc

Think of a train: when seats fill up, you add another coach.

#include <stdio.h>

#include <stdlib.h>

int main() {

    int *arr = malloc(5 * sizeof(int));

    for(int i=0;i<5;i++) arr[i]=i+1;

    int *tmp = realloc(arr, 10 * sizeof(int));

    if(tmp) arr = tmp;

    for(int i=5;i<10;i++) arr[i]=i+1;

    free(arr);

    return 0;

}

⚠️ Always use a temporary pointer with realloc to avoid memory leaks.

Common Array Operations

Linear Search

int linear_search(int arr[], int n, int key){

  for(int i=0;i<n;i++) if(arr[i]==key) return i;

  return -1;

}

Binary Search (Sorted Arrays)

int binary_search(int arr[], int n, int key) {

    int l=0, r=n-1;

    while(l<=r){

        int mid=l+(r-l)/2;

        if(arr[mid]==key) return mid;

        if(arr[mid]<key) l=mid+1; else r=mid-1;

    }

    return -1;

}

Sorting with qsort

#include <stdlib.h>

int cmp(const void *x, const void *y){ return (*(int*)x - (*(int*)y)); }

qsort(arr, n, sizeof(int), cmp);

Reverse an Array

for(int i=0;i<n/2;i++){

   int temp=arr[i];

   arr[i]=arr[n-i-1];

   arr[n-i-1]=temp;

}

Interview-Style Problems researched by Seed infotech 

Find Largest Element

Reverse an Array

Maximum Subarray Sum (Kadane’s Algorithm)

Rotate Array by k Elements

Try solving: Rotate [1,2,3,4,5,6,7] by k=3.

Common Mistakes & Pro Tips

❌ Accessing out-of-bounds (undefined behavior). ❌ Forgetting initialization. ❌ Assuming arrays resize automatically.

✅ Use const when array data should not change. ✅ Always check boundaries to avoid segmentation faults.

❓ FAQsQ1. What is an array in C programming? An array in C is a fixed-size collection of elements of the same type, stored in contiguous memory.

Q2. How do I declare a 2D array in C programming? Use int arr[2][3];. It’s stored row by row in memory.

Q3. Can I resize a normal array in C programming? No. Use dynamic arrays with malloc() and realloc().

Q4. What happens if I access arr[n]? It causes undefined behavior — may crash, corrupt memory, or give garbage output.

Q5. Why are arrays important for coding interviews? Arrays test how well you understand data organization, logic, and memory handling — skills that Seed Infotech helps students master through practical training.

Q6. Where can I practice arrays in real projects? At Seed Infotech, students apply arrays in hands-on projects like student record systems and sorting applications, making concepts easier to remember and implement.

Key Takeaways

Arrays = fast, contiguous memory storage.

Understand 1D, 2D, multi-D arrays.

Learn trade-offs: arrays vs pointers vs linked lists.

Use malloc / realloc for flexibility.

Practice common interview problems.

Wrap-up & Next Steps

Mastering arrays in C builds the foundation for algorithms, data structures, and job interviews.

5-Minute Challenge: Rotate an array by 2 positions and print the result.