Linear Search in Array in C: Program to Search an Element

Introduction

In this tutorial, we will learn how to write a C program to perform linear search in an array.

Linear search is the simplest searching algorithm. It works by checking each element of the array one by one from the beginning until the target element is found or the end of the array is reached.

Linear search is used in many real-world applications, such as:

• Finding a contact in an unsorted phonebook
• Searching for a product in a list
• Finding a student record by roll number
• Checking if a value exists in a dataset

C Program for Linear Search in Array

#include <stdio.h>

int main() {
    int n, i, search;
    int found = 0;  // Flag to track if element is found
    
    // Ask user for number of elements
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    // Declare array
    int arr[n];
    
    // Read elements into the array
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    // Get element to search
    printf("\nEnter the element to search: ");
    scanf("%d", &search);
    
    // Linear search
    for(i = 0; i < n; i++) {
        if(arr[i] == search) {
            printf("\nElement %d found at position %d (index %d)\n", 
                   search, i + 1, i);
            found = 1;
            break;  // Exit loop after finding first occurrence
        }
    }
    
    // If element not found
    if(found == 0) {
        printf("\nElement %d not found in the array.\n", search);
    }
    
    return 0;
}

Sample Output

Enter the number of elements: 6
Enter 6 elements:
10 20 30 40 50 60

Enter the element to search: 40

Element 40 found at position 4 (index 3)

When Element is Not Found:

Enter the number of elements: 5
Enter 5 elements:
10 20 30 40 50

Enter the element to search: 100

Element 100 not found in the array.

Example with Duplicate Elements:

Enter the number of elements: 7
Enter 7 elements:
10 20 10 30 10 40 50

Enter the element to search: 10

Element 10 found at position 1 (index 0)

Program Explanation

Let's break down the code step by step:

1. Include Header File: #include <stdio.h> includes the standard input/output library.
2. Declare Variables:
   • int n; — number of elements
   • int i; — loop counter
   • int search; — element to search for
   • int found = 0; — flag (0 = not found, 1 = found)
3. Get User Input: Reads the array elements from the user.
4. Get Search Element: Asks the user for the element to search.
5. Linear Search:
   • The for loop iterates through each element
   • If arr[i] == search, the element is found
   • Prints the position and index
   • Sets found = 1 and breaks out of the loop
6. Handle Not Found: If found == 0, prints "Element not found".
7. Return: return 0; indicates successful program execution.

Linear Search Algorithm

Step-by-step algorithm:

1. Start
2. Read the array elements
3. Read the element to search (target)
4. Set found = 0
5. For i = 0 to n-1:
   • If arr[i] == target:
     • Print "Element found at position i+1"
     • Set found = 1
     • Break the loop
6. If found == 0:
   • Print "Element not found"
7. End

Visual Example

Searching for 40 in the array [10, 20, 30, 40, 50]:

Linear Search Using Function

Here's a version using a separate function for better code organization:

#include <stdio.h>

int linearSearch(int arr[], int n, int search) {
    for(int i = 0; i < n; i++) {
        if(arr[i] == search) {
            return i;  // Return index if found
        }
    }
    return -1;  // Return -1 if not found
}

int main() {
    int n, search, result;
    
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    int arr[n];
    
    printf("Enter %d elements:\n", n);
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    printf("\nEnter the element to search: ");
    scanf("%d", &search);
    
    result = linearSearch(arr, n, search);
    
    if(result != -1) {
        printf("\nElement %d found at position %d (index %d)\n", 
               search, result + 1, result);
    } else {
        printf("\nElement %d not found in the array.\n", search);
    }
    
    return 0;
}

Time and Space Complexity

#include <stdio.h>

int main() {
    int n, i, search;
    int count = 0;
    
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    int arr[n];
    
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    printf("\nEnter the element to search: ");
    scanf("%d", &search);
    
    // Count occurrences
    for(i = 0; i < n; i++) {
        if(arr[i] == search) {
            count++;
        }
    }
    
    if(count > 0) {
        printf("\nElement %d found %d time(s) in the array.\n", search, count);
    } else {
        printf("\nElement %d not found in the array.\n", search);
    }
    
    return 0;
}

Frequently Asked Questions

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