# C Program for Insertion Sort

Insertion sort in C: Insertion sort is a simple sorting algorithm that builds the final sorted array (or list) one item at a time. It is Adaptive, i.e., efficient for data sets that are already substantially sorted: the time complexity is O(kn) when each element in the input is no more than k places away from its sorted position. It is much less efficient on large lists than more advanced algorithms such as quicksort, heapsort, or merge sort.
• Worst complexity: n2
• Average complexity: n2
• Best complexity: n
• Space complexity: 1

Problem: Sort a random array of n integers (accept the value of n from user) in ascending order by using insertion sort algorithm

## C program for insertion sort

``````// Aim: C program for insertion sort

#include <stdio.h>
#include <math.h>

/* Function to sort an array using insertion sort*/

void insertionSort(int arr[], int n)
{
int i, key, j;
for (i = 1; i < n; i++)
{
key = arr[i];
j = i-1;

/* Move elements of arr[0..i-1], that are
greater than key, to one position ahead
of their current position */

while (j >= 0 && arr[j] < key)
{
arr[j+1] = arr[j];
j = j-1;
}
arr[j+1] = key;
}
}

// A utility function to print an array of size n
void printArray(int arr[], int n)
{
int i;
for (i=0; i < n; i++)
printf("%d ", arr[i]);
printf("\n");
}

/* Driver program to test insertion sort */
int main()
{
int arr[] = {12, 11, 13, 5, 6};
int n = sizeof(arr)/sizeof(arr);

insertionSort(arr, n);
printArray(arr, n);

return 0;
}

``````
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Problem: Sort a random array of n integers (accept the value of n from user) in ascending order by using insertion sort algorithm.

## C program to sort a random array in ascending order using insertion sort

``````/* Aim: C Program to sort a random array in ascending order using insertion sort */

#include
#include

// Function to display array

void DisplayArray(int arr[],int n)
{
int i;

for(i=0;i<n;i++)
printf(" %d ",arr[i]);
}

// Function to generate random array

void Generate(int *arr, int n)
{
int i;

for(i=0;i<n;i++)
arr[i]=rand()%100;

}

// Function for insertion sort

void InsertionSort(int arr[], int n)
{

int Rvalue,i,j;

for(i=1;i<n;i++)
{

Rvalue=arr[i];

j=i-1;

while( j>=0 && arr[j]>Rvalue)
{
arr[j+1]=arr[j];
j=j-1;
}

arr[j+1]=Rvalue;

}
}

// main() function to test the insertion sort

void main()
{
int arr,n;

printf("\n Enter the size of array:- ");
scanf("%d",&n);

Generate(arr,n); // Generating a random array

printf("\n The random array: ");
DisplayArray(arr,n); // Displaying the array

InsertionSort(arr,n); // Sorting the array

printf("\n The sorted array: ");
DisplayArray(arr,n); // Displaying the sorted array

printf("\n");

}

/* Output of above code:-

Enter the size of array:- 5

The random array:  83 86 77 15 93

The sorted array:  15 77 83 86 93

*/``````
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Problem: Sort a random array in descending order using insertion sort.

Que. What modification is required to insertion sort to sort the integers in descending order?
Answer: We just have check whether the integer before key is less than key or not. If it is, we have to swap it.

## C program to sort random array in descending order using insertion sort

``````/* C Program to sort a random array in descending order using insertion sort */

#include<stdio.h>
#include<stdlib.h>

void DisplayArray(int arr[],int n)
{
int i;

for(i=0;i<n;i++)
printf(" %d ",arr[i]);
}

void Generate(int *arr, int n)
{
int i;

for(i=0;i<n;i++)
arr[i]=rand()%100;
}

void InsertionSort(int arr[], int n)
{

int Key,i,j;

for(i=1;i<n;i++)
{

Key=arr[i];

j=i-1;

while( j>=0 && arr[j]<Key)
{
arr[j+1]=arr[j];
j=j-1;
}

arr[j+1]=Key;
}
}

int main()
{
int arr,n;

printf("\n Enter the size of array:- ");
scanf("%d",&n);

Generate(arr,n); // Generating a random array

printf("\n The random array: ");
DisplayArray(arr,n); // Displaying the array

InsertionSort(arr,n); // Sorting the array

printf("\n The sorted array: ");
DisplayArray(arr,n); // Displaying the sorted array

printf("\n");

return 0;
}

/* Output of above code:-

Enter the size of array:- 5

The random array:  83  86  77  15  93
The sorted array:  93  86  83  77  15

*/``````
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