Merge Sort

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

void merge(int leftArr[], int rightArr[], int mainArray[], int leftLength, int rightLength){
    int leftIndex, rightIndex, mainIndex;
    leftIndex = rightIndex = mainIndex = 0;
    while(leftIndex < leftLength && rightIndex < rightLength){
        if(leftArr[leftIndex] < rightArr[rightIndex]){
            mainArray[mainIndex] = leftArr[leftIndex];
            leftIndex++;
        }
        else{
            mainArray[mainIndex] = rightArr[rightIndex];
            rightIndex++;
        }
        mainIndex++;
    }

    while(leftIndex < leftLength){
        mainArray[mainIndex] = leftArr[leftIndex];
        mainIndex++;
        leftIndex++;
    }

    while(rightIndex < rightLength){
        mainArray[mainIndex] = rightArr[rightIndex];
        mainIndex++;
        rightIndex++;
    }
    printf("\nMerge:\n");
    printArr(mainArray, leftLength+rightLength);
    printf("\n");
}

void mergeSort(int mainArr[], int mainArrLength){
    int index = 0;
    if(mainArrLength < 2){
        return;
    }
    int midIndex = mainArrLength/2;
    int* leftArr = (int*)malloc(midIndex * sizeof(int));
    int* rightArr = (int*)malloc((mainArrLength - midIndex) * sizeof(int));
    for(index=0; index<midIndex; index++){
        leftArr[index] = mainArr[index];
    }
    printf("Left Array: \n");
    printArr(leftArr,midIndex);
    for(index=midIndex; index < mainArrLength; index++){
        rightArr[index - midIndex] = mainArr[index];
    }
    printf("Right Array: \n");
    printArr(rightArr, midIndex);
    mergeSort(leftArr, midIndex);
    mergeSort(rightArr, mainArrLength - midIndex);
    merge(leftArr, rightArr, mainArr, midIndex, mainArrLength - midIndex);
    return;
}

void printArr(int ArrToPrint[], int lengthArr){
    int index;
    for(index=0; index<lengthArr; index++){
        printf("%d ",ArrToPrint[index]);
    }
    printf("\n");
}

int main()
{
    int mainArr[] = {2, 4, 1, 6, 8, 5, 3, 7};
    int index = 0;
    int lengthArr = sizeof(mainArr)/sizeof(mainArr[0]);
    printf("Before Sorting: \n");
    printArr(mainArr, lengthArr);
    printf("====================== Sorting Begins =====================\n\n");
    mergeSort(mainArr, lengthArr);
    printf("After Sorting: \n");
    printArr(mainArr, lengthArr);
    return 0;
}