Analyze this code and input descriptive comments explaining what is happening in

Question

Analyze this code and input descriptive comments explaining what is happening in clear english

please provide comments only on code after the line

void merge(int a[],int i1,int j1,int i2,int j2)

the entire code is as follows

#include<stdio.h>

void mergesort(int a[],int i,int j);
void merge(int a[],int i1,int j1,int i2,int j2);

int main()
{
int a[30],n,i;
printf("Enter no of elements:");
scanf("%d",&n);
printf("Enter array elements:");
  
for(i=0;i<n;i++)
scanf("%d",&a[i]);
  
mergesort(a,0,n-1);
  
printf(" Sorted array is :");
for(i=0;i<n;i++)
printf("%d ",a[i]);
  
return 0;
}

void mergesort(int a[],int i,int j)
{
int mid;
  
if(i<j)
{
mid=(i+j)/2;
mergesort(a,i,mid);   
mergesort(a,mid+1,j);
merge(a,i,mid,mid+1,j);
}
}

void merge(int a[],int i1,int j1,int i2,int j2)
{
int temp[50]; //array used for merging
int i,j,k;
i=i1; //beginning of the first list
j=i2; //beginning of the second list
k=0;
  
while(i<=j1 && j<=j2)
{
if(a[i]<a[j])
temp[k++]=a[i++];
else
temp[k++]=a[j++];
}
  
while(i<=j1)
temp[k++]=a[i++];
  
while(j<=j2)
temp[k++]=a[j++];
  
//Transfer elements from temp[] back to a[]
for(i=i1,j=0;i<=j2;i++,j++)
a[i]=temp[j];
}

Explanation / Answer

#include<stdio.h>

void mergesort(int a[],int i,int j);
void merge(int a[],int i1,int j1,int i2,int j2);

int main()
{
int a[30],n,i; // declaring variables
printf("Enter no of elements:");
scanf("%d",&n); // reading no. of elements
printf("Enter array elements:");

for(i=0;i<n;i++)
scanf("%d",&a[i]); // reading array elements from user

// calling mergesort() with the array, the lower limit and the upper limit
mergesort(a,0,n-1);

printf(" Sorted array is :");
for(i=0;i<n;i++)
printf("%d ",a[i]); // printing array elements

return 0;
}

void mergesort(int a[],int i,int j)
{
/* Merge sort is a divide and conquer technique to sort an array.
* It first divides the array in two halves and sort each half
* separately and then merges the two halves into one.
* Now, after dividing the array into two halves, it follows the
* aforesaid method on each of the half i.e., it repeats the divide
* and sort then merge process on each of the halves created until
* the halves cannot the divided anymore. After that, it starts merging
* them. Merge sort uses recursion technique to achieve it's goal.
*/
int mid; // mid will hold the middle point of the array

if(i<j) // recursion will be done only if lower limit is smaller than upper limit
// i: lower limit, j: upper limit
{
mid=(i+j)/2; // calculating mid point of array
mergesort(a,i,mid); // calling mergesort() on first half of the array to sort
mergesort(a,mid+1,j); // calling mergesort() on last half of the array to sort
merge(a,i,mid,mid+1,j); // after sorting separate halves, merge() will merge the two halves
}
}

void merge(int a[],int i1,int j1,int i2,int j2)
{
int temp[50]; //array used for merging
int i,j,k;
i=i1; //beginning of the first list
j=i2; //beginning of the second list
k=0;

//j1 holds end of first list, j2 holds end of second list
while(i<=j1 && j<=j2) // when lower limits of both lists will not cross the upper limits
{
if(a[i]<a[j]) // if element from first list is smaller than element from second list
temp[k++]=a[i++]; // then store element from first list first
else
temp[k++]=a[j++]; // else store element from second list first
}

// when one of the two lists exhausted while merging, then the remaining elements
// from the other list should be inserted after them

while(i<=j1) // if first list has not been exhausted
temp[k++]=a[i++]; // insert them into the array

while(j<=j2) // if second list has not been exhausted
temp[k++]=a[j++]; // insert them into the array

//Transfer elements from temp[] back to a[]
for(i=i1,j=0;i<=j2;i++,j++)
a[i]=temp[j];
}

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