Code

 #include <stdio.h>

#include <stdlib.h>

// Function to merge two subarrays of arr[]

void merge(int arr[], int left, int middle, int right) {

    int i, j, k;

    int n1 = middle - left + 1;

    int n2 = right - middle;

    // Create temporary arrays

    int L[n1], R[n2];

    // Copy data to temporary arrays L[] and R[]

    for (i = 0; i < n1; i++)

        L[i] = arr[left + i];

    for (j = 0; j < n2; j++)

        R[j] = arr[middle + 1 + j];

    // Merge the temporary arrays back into arr[l..r]

    i = 0; // Initial index of first subarray

    j = 0; // Initial index of second subarray

    k = left; // 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++;

    }

}

// Main function to perform merge sort on arr[l..r]

void mergeSort(int arr[], int left, int right) {

    if (left < right) {

        // Same as (left+right)/2, but avoids overflow for large left and right

        int middle = left + (right - left) / 2;

        // Sort first and second halves

        mergeSort(arr, left, middle);

        mergeSort(arr, middle + 1, right);

        // Merge the sorted halves

        merge(arr, left, middle, right);

    }

}

// Example usage

int main() {

    int arr[] = {12, 11, 13, 5, 6, 7};

    int arr_size = sizeof(arr) / sizeof(arr[0]);

    printf("Given array is \n");

    for (int i = 0; i < arr_size; i++)

        printf("%d ", arr[i]);

    mergeSort(arr, 0, arr_size - 1);

    printf("\nSorted array is \n");

    for (int 

i = 0; i < arr_size; i++)

        printf("%d ", arr[i]);

    return 0;

}