C Exercises: Count the total number of duplicate elements in an array

Last update on July 31 2025 13:03:36 (UTC/GMT +8 hours)

5. Count Duplicate Elements

Write a program in C to count the total number of duplicate elements in an array.

The task involves writing a C program to count the number of duplicate elements in an array. The program will take a specified number of integer inputs, store them in an array, and then determine and display how many elements appear more than once.

Visual Presentation:

C Exercises: Count a total number of duplicate elements in an array

Pseudo code to count the total number of duplicate elements in an array:

Initialize a variable 'count' to 0.
Read the array size, 'n'.
Declare an integer array of size 'n'.
Read the array elements.
Loop through each element of the array from index 0 to n-2: a. Loop through the remaining elements of the array from index i+1 to n-1: i. If the current element and any of the remaining elements are equal, increment the 'count' variable and break out of the inner loop.
Print the value of 'count' as the total number of duplicate elements in the array.
End

Sample Solution:

C Code:

#include <stdio.h>
// Main function
int main()
{
    int arr[100];  // Declare an array of size 100 to store integer values
    int n, mm = 1, ctr = 0;  // Declare variables to store array size, mm (unused), and duplicate counter
    int i, j;  // Declare loop counters
    // Prompt the user to input the number of elements to be stored in the array
    printf("Input the number of elements to be stored in the array :");
    scanf("%d", &n);
    // Prompt the user to input n elements into the array
    printf("Input %d elements in the array :\n", n);
    for (i = 0; i < n; i++)
    {
        printf("element - %d : ", i);
        scanf("%d", &arr[i]);  // Read the input and store it in the array
    }
    // Check for duplicate elements in the array using nested loops
    for (i = 0; i < n; i++)
    {
        for (j = i + 1; j < n; j++)
        {
            if (arr[i] == arr[j])
            {
                ctr++;  // Increment the duplicate counter if a duplicate is found
                break;  // Exit the inner loop as soon as a duplicate is found
            }
        }
    }
    // Display the total number of duplicate elements found in the array
    printf("Total number of duplicate elements found in the array: %d\n", ctr);
    return 0;  // Return 0 to indicate successful execution
}

Sample Output:

Input the number of elements to be stored in the array :5
Input 5 elements in the array :
element - 0 : 1
element - 1 : 1
element - 2 : 2
element - 3 : 3
element - 4 : 3
Total number of duplicate elements found in the array: 2

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to count the number of duplicate elements in an array without using additional arrays.
Write a C program to list duplicate elements along with their frequency from an array.
Write a C program to identify the first duplicate element encountered in an array.
Write a C program to count duplicates using a hash table approach with dynamic memory allocation.

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