Bubble sort algorithm in c

/* Bubble sort code */ #include <stdio.h> int main(){
  int array[100], n, c, d, swap;   printf("Enter number of elements\n");
  scanf("%d", &n);   printf("Enter %d integers\n", n);   for (c = 0; c < n; c++)
    scanf("%d", &array[c]);   for (c = 0 ; c < ( n - 1 ); c++)
  {
    for (d = 0 ; d < n - c - 1; d++)
    {
      if (array[d] > array[d+1]) /* For decreasing order use < */
      {
        swap       = array[d];
        array[d]   = array[d+1];
        array[d+1] = swap;
      }
    }
  }   printf("Sorted list in ascending order:\n");

MergeSort

MergeSort is a Divide and Conquer algorithm.  It divides input array in two halves, calls itself for the two halves and then merges the two sorted halves. The merg() function is used for merging two halves.  The merge(arr, l, m, r) is key process that assumes that arr[l..m] and arr[m+1..r] are sorted and merges the two sorted sub-arrays into one. See following C implementation for details.

MergeSort(arr[], l,  r)If r > l     1. Find the middle point to divide the array into two halves:  
             middle m = (l+r)/2     2. Call mergeSort for first half:   
             Call mergeSort(arr, l, m)     3. Call mergeSort for second half:
             Call mergeSort(arr, m+1, r)     4. Merge the two halves sorted in step 2 and 3:
             Call merge(arr, l, m, r)

The following diagram from wikipedia shows the complete merge sort process for an example array {38, 27, 43, 3, 9, 82, 10}. If we take a closer look at the diagram, we can see that the array is recursively divided in two halves till the size becomes 1. Once the size becomes 1, the merge processes comes into action and starts merging arrays back till the complete array is merged.

Merge-Sort

C/C++

/* C program for Merge Sort */
#include<stdlib.h>
#include<stdio.h>
 
// Merges two subarrays of arr[].
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void merge( int arr[], int l, int m, int r)
{
     int i, j, k;
     int n1 = m - l + 1;
     int n2 =  r - m;
 
     /* create temp arrays */
     int L[n1], R[n2];
 
     /* Copy data to temp arrays L[] and R[] */
     for (i = 0; i < n1; i++)
         L[i] = arr[l + i];
     for (j = 0; j < n2; j++)
         R[j] = arr[m + 1+ j];
 
     /* Merge the temp arrays back into arr[l..r]*/
     i = 0; // Initial index of first subarray
     j = 0; // Initial index of second subarray
     k = l; // Initial index of merged subarray
     while (i < n1 && j < n2)
     {
         if (L[i] <= R[j])
         {
             arr[k] = L[i];
             i++;
         }
         else
         {
             arr[k] = R[j];
             j++;
         }
         k++;
     }
 
     /* Copy the remaining elements of L[], if there
        are any */
     while (i < n1)
     {
         arr[k] = L[i];
         i++;
         k++;
     }
 
     /* Copy the remaining elements of R[], if there
        are any */
     while (j < n2)
     {
         arr[k] = R[j];
         j++;
         k++;
     }
}
 
/* l is for left index and r is right index of the
    sub-array of arr to be sorted */
void mergeSort( int arr[], int l, int r)
{
     if (l < r)
     {
         // Same as (l+r)/2, but avoids overflow for
         // large l and h
         int m = l+(r-l)/2;
 
         // Sort first and second halves
         mergeSort(arr, l, m);
         mergeSort(arr, m+1, r);
 
         merge(arr, l, m, r);
     }
}
 
/* UTILITY FUNCTIONS */
/* Function to print an array */
void printArray( int A[], int size)
{
     int i;
     for (i=0; i < size; i++)
         printf ( "%d " , A[i]);
     printf ( "\n" );
}
 
/* Driver program to test above functions */
int main()
{
     int arr[] = {12, 11, 13, 5, 6, 7};
     int arr_size = sizeof (arr)/ sizeof (arr[0]);
 
     printf ( "Given array is \n" );
     printArray(arr, arr_size);
 
     mergeSort(arr, 0, arr_size - 1);
 
     printf ( "\nSorted array is \n" );
     printArray(arr, arr_size);
     return 0;
}