🚀 DSA with C – Day 2: Arrays & Linear Search

 

🎯 Goal:

• Understand arrays in C.

• Learn how to use loops with arrays.

• Implement Linear Search algorithm.

• Practice multiple array-based programs.

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🧠 Theory: What is an Array?

• An array is a collection of elements stored in contiguous memory.

• All elements must be of the same type.

• Indexing starts from 0 in C.

🔧 Declaration and Initialization

int arr[5];             // Declaration
int arr[5] = {1, 2, 3, 4, 5};  // Initialization

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👨‍💻 Basic Program: Input & Output in Arrays

#include <stdio.h>

int main() {
    int arr[5];
    printf("Enter 5 numbers:\n");
    for (int i = 0; i < 5; i++) {
        scanf("%d", &arr[i]);
    }

    printf("You entered:\n");
    for (int i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

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🔍 Linear Search in C

➕ Problem: Given an array and a number x, find if x exists in the array.

✅ Code:

#include <stdio.h>

int main() {
    int arr[100], n, x, found = 0;
    printf("Enter number of elements: ");
    scanf("%d", &n);

    printf("Enter %d elements:\n", n);
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    printf("Enter element to search: ");
    scanf("%d", &x);

    for (int i = 0; i < n; i++) {
        if (arr[i] == x) {
            printf("Element found at index %d\n", i);
            found = 1;
            break;
        }
    }

    if (!found)
        printf("Element not found\n");

    return 0;
}

🧠 Time Complexity:

• Best case: O(1)

• Worst case: O(n)

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🧪 Practice Problems:

1. Find the maximum and minimum element in an array.

2. Count how many times a given number appears in the array.

3. Reverse an array.

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📘 Homework for Day 2:

• Write a program to copy one array to another.

• Write a program to merge two arrays.

• Try solving one problem from LeetCode Easy using arrays (optional but forward-thinking!).

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📅 Day 2 Summary

• ✅ Learned arrays

• ✅ Implemented Linear Search

• ✅ Practiced I/O and traversal

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🧭 Tomorrow: Sorting (Bubble Sort) + Binary Search

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