Frequency of Each Element in Array in C: Program to Find Occurrence of Elements

Introduction

In this tutorial, we will learn how to write a C program to find the frequency or occurrence of each element in an array.

Finding the frequency of elements in an array is a common programming task. It is used in many real-world applications, such as:

• Finding the most frequent number in a dataset
• Analyzing survey responses
• Counting word occurrences in text processing
• Identifying duplicate values in a list

C Program to Find Frequency of Each Element in Array

#include <stdio.h>

int main() {
    int n, i, j;
    int count;
    
    // Ask user for number of elements
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    // Declare array of size n
    int arr[n];
    // Declare visited array to track counted elements
    int visited[n];
    
    // Initialize visited array with 0
    for(i = 0; i < n; i++) {
        visited[i] = 0;
    }
    
    // Read elements into the array
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    // Find frequency of each element
    printf("\nFrequency of each element:\n");
    for(i = 0; i < n; i++) {
        // Skip if element is already counted
        if(visited[i] == 1) {
            continue;
        }
        
        count = 1;
        for(j = i + 1; j < n; j++) {
            if(arr[i] == arr[j]) {
                count++;
                visited[j] = 1;  // Mark as visited
            }
        }
        
        printf("%d occurs %d times\n", arr[i], count);
    }
    
    return 0;
}

Sample Output

Enter the number of elements: 8
Enter 8 elements:
10 20 30 10 20 10 40 30

Frequency of each element:
10 occurs 3 times
20 occurs 2 times
30 occurs 2 times
40 occurs 1 times

Another Example:

Enter the number of elements: 6
Enter 6 elements:
5 5 5 5 5 5

Frequency of each element:
5 occurs 6 times

Example with Negative Numbers:

Enter the number of elements: 7
Enter 7 elements:
-5 10 -5 20 -5 10 30

Frequency of each element:
-5 occurs 3 times
10 occurs 2 times
20 occurs 1 times
30 occurs 1 times

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; — stores the number of elements
   • int i, j; — loop counters
   • int count; — stores the frequency of each element
3. Declare Arrays:
   • int arr[n]; — the main array
   • int visited[n]; — keeps track of elements that have already been counted
4. Initialize Visited Array: The for loop sets all elements of visited to 0 (not counted yet).
5. Get User Input: Prompts the user to enter the number of elements and then reads them into the array.
6. Find Frequency: The outer loop for(i = 0; i < n; i++) iterates through each element:
   • If visited[i] == 1, the element has already been counted, so skip it.
   • Otherwise, set count = 1 and compare arr[i] with all later elements using the inner loop.
   • If a match is found, increment count and mark visited[j] = 1.
7. Display Result: Prints each unique element and its frequency.
8. Return: return 0; indicates successful program execution.

Algorithm to Find Frequency of Elements

1. Start
2. Read the number of elements (n)
3. Read n elements into the array arr
4. Initialize visited array with 0
5. For i = 0 to n-1:
   • If visited[i] == 0:
     • Set count = 1
     • For j = i+1 to n-1:
       • If arr[i] == arr[j]:
         • count++
         • Set visited[j] = 1
     • Print arr[i] and count
6. End

Alternative Method: Using Sorting

Another approach to find frequency is to sort the array first, then count consecutive equal elements. This method can be more efficient for large arrays.

#include <stdio.h>

int main() {
    int n, i, j, count;
    
    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]);
    }
    
    // Simple bubble sort to sort the array
    for(i = 0; i < n-1; i++) {
        for(j = 0; j < n-i-1; j++) {
            if(arr[j] > arr[j+1]) {
                int temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
    
    // Count frequency of each element
    printf("\nFrequency of each element:\n");
    for(i = 0; i < n; i = i + count) {
        count = 1;
        for(j = i + 1; j < n && arr[j] == arr[i]; j++) {
            count++;
        }
        printf("%d occurs %d times\n", arr[i], count);
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int n, i, j;
    int max_freq = 0, most_frequent_element;
    
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    int arr[n];
    int visited[n];
    
    for(i = 0; i < n; i++) {
        visited[i] = 0;
    }
    
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    for(i = 0; i < n; i++) {
        if(visited[i] == 1) {
            continue;
        }
        
        int count = 1;
        for(j = i + 1; j < n; j++) {
            if(arr[i] == arr[j]) {
                count++;
                visited[j] = 1;
            }
        }
        
        if(count > max_freq) {
            max_freq = count;
            most_frequent_element = arr[i];
        }
    }
    
    printf("\nMost frequent element: %d (appears %d times)\n", 
           most_frequent_element, max_freq);
    
    return 0;
}

Frequently Asked Questions

Previous Topic: -->> Print Negative Elements in Array   ||   Next topic: -->> Reverse an Array in C