C program to delete duplicate elements from array

Write a C program to delete duplicate elements from array. How to remove duplicate elements from array in C programming. After performing delete operation the array should only contain unique integer value. Logic to delete duplicate elements from array.

Input array elements: 10, 20, 10, 1, 100, 10, 2, 1, 5, 10

After removing all duplicate elements
Elements of array are: 10, 20, 1, 100, 2, 5

Required knowledge

Basic Input Output, If else, For loop, Nested loop, Array

Logic to delete duplicate elements from array

Step by step descriptive logic to delete duplicate elements from array.

1. Input size and elements in array from user. Store it in some variable say size and arr.
2. To find duplicate elements in given array we need two loops. Run an outer loop from 0 to size. Loop structure must look like for(i=0; i<size; i++). This loop is used to select each element of array and check next subsequent elements for duplicates using another nested loop.
3. Run another inner loop to find first duplicate of current element. Run an inner loop from i + 1 to size. The loop structure should look like for(j=i+1; j<size; j++).
4. Inside the inner loop check for duplicate element. If a duplicate element is found then delete that array element. Also if a duplicate element is found then decrement size of array i.e. size = size - 1.

Learn more about program to find unique elements in array.

Program to delete duplicate elements from array

/**
 * C program to delete all duplicate elements from array
 */

#include <stdio.h>

#define MAX_SIZE 100 // Maximum size of the array

int main()
{
    int arr[MAX_SIZE]; // Declares an array of size 100
    int size;          // Total number of elements in array
    int i, j, k;       // Loop control variables

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

    /* Input elements in the array */
    printf("Enter elements in array : ");
    for(i=0; i<size; i++)
    {
        scanf("%d", &arr[i]);
    }


    /*
     * Find duplicate elements in array
     */
    for(i=0; i<size; i++)
    {
        for(j=i+1; j<size; j++)
        {
            /* If any duplicate found */
            if(arr[i] == arr[j])
            {
                /* Delete the current duplicate element */
                for(k=j; k < size - 1; k++)
                {
                    arr[k] = arr[k + 1];
                }

                /* Decrement size after removing duplicate element */
                size--;

                /* If shifting of elements occur then don't increment j */
                j--;
            }
        }
    }


    /*
     * Print array after deleting duplicate elements
     */
    printf("\nArray elements after deleting duplicates : ");
    for(i=0; i<size; i++)
    {
        printf("%d\t", arr[i]);
    }

    return 0;
}

Enter size of the array : 10
Enter elements in array : 10 20 10 1 100 10 2 1 5 10

Array elements after deleting duplicates : 10    20    1    100    2    5

Happy coding 😉