Sort Array in Descending Order in C: Program to Sort Array Elements

Introduction

In this tutorial, we will learn how to write a C program to sort an array in descending order.

Sorting an array in descending order means arranging elements from largest to smallest. This is useful in many real-world applications, such as:

• Ranking students by highest marks
• Listing products by highest price
• Displaying top scores in a game
• Sorting salaries from highest to lowest

C Program to Sort Array in Descending Order (Using Bubble Sort)

#include <stdio.h>

int main() {
    int n, i, j, temp;
    
    // 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]);
    }
    
    // Bubble sort - sort in descending order
    for(i = 0; i < n-1; i++) {
        for(j = 0; j < n-i-1; j++) {
            if(arr[j] < arr[j+1]) {  // Compare for descending
                // Swap arr[j] and arr[j+1]
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
    
    // Display sorted array
    printf("\nArray in descending order: ");
    for(i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    
    return 0;
}

Sample Output

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

Array in descending order: 60 50 40 30 20 10

Another Example:

Enter the number of elements: 5
Enter 5 elements:
25 10 35 15 20

Array in descending order: 35 25 20 15 10

Example with Negative Numbers:

Enter the number of elements: 7
Enter 7 elements:
-5 10 -2 8 0 -10 3

Array in descending order: 10 8 3 0 -2 -5 -10

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 temp; — temporary variable for swapping
3. Get User Input: Prompts the user to enter the number of elements and then reads them into the array.
4. Bubble Sort in Descending Order:
   • Outer Loop: for(i = 0; i < n-1; i++) — runs n-1 times
   • Inner Loop: for(j = 0; j < n-i-1; j++) — compares adjacent elements
   • Comparison: If arr[j] < arr[j+1], swap them (this puts larger elements first)
   • After each pass, the smallest element "bubbles down" to the end
5. Display Result: Prints the sorted array in descending order.
6. Return: return 0; indicates successful program execution.

Bubble Sort Algorithm for Descending Order

Step-by-step explanation of descending bubble sort:

1. Start with the first element
2. Compare the current element with the next element
3. If the current element is smaller than the next element, swap them
4. Move to the next element and repeat step 2-3
5. After one complete pass, the smallest element is at the end
6. Repeat the process for the remaining elements (excluding the last)
7. Stop when all elements are sorted in descending order

Visual Example

Let's see how descending bubble sort works on the array [50, 20, 40, 10, 30]:

Optimized Descending Bubble Sort

We can optimize bubble sort by adding a flag to check if any swaps were made in a pass. If no swaps were made, the array is already sorted and we can break early.

#include <stdio.h>

int main() {
    int n, i, j, temp;
    int swapped;
    
    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]);
    }
    
    // Optimized descending bubble sort
    for(i = 0; i < n-1; i++) {
        swapped = 0;
        for(j = 0; j < n-i-1; j++) {
            if(arr[j] < arr[j+1]) {  // Compare for descending
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
                swapped = 1;
            }
        }
        // If no swaps were made, array is already sorted
        if(swapped == 0) {
            break;
        }
    }
    
    printf("\nArray in descending order: ");
    for(i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    
    return 0;
}

Ascending vs Descending Order

#include <stdio.h>

int main() {
    int n, i, j, temp;
    int choice;
    
    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("\nChoose sorting order:\n");
    printf("1. Ascending\n");
    printf("2. Descending\n");
    printf("Enter your choice: ");
    scanf("%d", &choice);
    
    for(i = 0; i < n-1; i++) {
        for(j = 0; j < n-i-1; j++) {
            if(choice == 1) {
                // Ascending
                if(arr[j] > arr[j+1]) {
                    temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                }
            } else {
                // Descending
                if(arr[j] < arr[j+1]) {
                    temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                }
            }
        }
    }
    
    printf("\nSorted array: ");
    for(i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    
    return 0;
}

Frequently Asked Questions

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