C program to search element in array using pointers

Write a C program to input elements in array and search an element in array using pointers. How to search an element in array using pointers in C programming. Logic to search an element in array using pointers in C program.

Example

Input

Input array elements: 10 20 30 40 50 60 70 80 90 100
Input element to search: 25

Output

25 does not exists in array.

Required knowledge

Basic C programming, Array, Functions, Pointer, Pointer Arithmetic, Pointer and Arrays

In my previous posts related to array, I have explained how easily we can search an element in array without using pointer. Here in this post we will see how to search an element in array using pointer.

Logic to search an element in array using pointers

Below is the step by step descriptive logic to search an element in array using pointer.

  1. Input size and elements in array. Store them in some variable say size and array.
  2. Input element to search from user, store it in another variable say toSearch.
  3. Initialize a pointer to first and last element of array. Say arr = array and arrEnd = (array + size - 1).
  4. Initialize a variable index = 0 that will keep track of searched element index.
  5. For each array element increment index and arr by 1 till arr <= arrEnd and *arr != toSearch.
  6. Finally if (arr <= arrEnd), then toSearch element exists in array at position index + 1 otherwise not.

Program to search an element in array using pointers

/**
 * C program to search an element in array using pointers
 */

#include <stdio.h>

#define MAX_SIZE 100


/* Function declaration */
void inputArray(int * arr, int size);
int search(int * arr, int size, int toSearch);



int main()
{
    int array[MAX_SIZE];
    int size, toSearch, searchIndex;


    /*
     * Input size and elements in array
     */
    printf("Enter size of array: ");
    scanf("%d", &size);

    printf("Enter elements in array: ");
    inputArray(array, size);


    // Input element to search from user
    printf("Enter element to search: ");
    scanf("%d", &toSearch);


    // Call search funtion to search element in array
    searchIndex = search(array, size, toSearch);


    // Print search results
    if(searchIndex == -1)
        printf("%d does not exists in array.", toSearch);
    else
        printf("%d is found at %d position.", toSearch, searchIndex + 1);


    return 0;
}




/**
 * Function to input elements in array.
 *
 * @arr     Pointer to integer array
 * @size    Size of the array
 */
void inputArray(int * arr, int size)
{
    // Pointer to last array element arr[0]
    int * arrEnd = (arr + size - 1);


    // Run loop till last array element
    while(arr <= arrEnd)
    {
        scanf("%d", arr++);
    }
}




/**
 * Function to perform linear search in array. The function
 * returns an integer between 0 to size-1 specifying first 
 * index of successful searched element in array.
 *
 * @arr      Pointer to integer array.
 * @size     Size of the array.
 * @toSearch Element to search within array.
 *
 * @return   Returns -1 if element does not exists in array, 
 *           otherwise returns element index.
 */
int search(int * arr, int size, int toSearch)
{
    int index = 0;

    // Pointer to last array element arr[size - 1]
    int * arrEnd = (arr + size - 1);

    /*
     * Run a loop from start of array to last array element (arr <= arrEnd), 
     * until current array element does not match element to search.
     */
    while(arr <= arrEnd && *arr != toSearch) {
        arr++;
        index++;
    }


    // If element is found
    if(arr <= arrEnd)
        return index;
    
    return -1;
}

You can further optimize the above program by removing the unwanted index variable from search() function. Below is another implementation of search() function without index variable.

int search(int * arr, int size, int toSearch)
{
    // Pointer to last array element arr[size - 1]
    int * arrEnd = (arr + size - 1);
    
    while(arr <= arrEnd && *arr != toSearch) arr++;
    
    // If element is found
    if(arr <= arrEnd)
        return (arrEnd - arr) / sizeof(int) + 1;

    return -1;
}

Output

Enter size of array: 10
Enter elements in array: 10 20 30 40 50 60 70 80 90 100
Enter element to search: 30
30 is found at 3 position.

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