Function to convert (long long) integers to strings with thousand comma separators

PrettyNumbers.c

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

char *PrettyNumbers(long long int inputBytes)
{
    double tempVar = log10((double) inputBytes);
    int noElements = (int) floor(tempVar / 3.0), n, remn = (int) (tempVar + 1) % 3;
    char *output, tempString[4];
    
    if (remn == 0)
        remn = 3;
    
    output = malloc(sizeof(char) * ((int) ceil(tempVar) + 1 + noElements));
    memset(output, 0, (int) floor(tempVar) + 2);
    
    for (n = noElements - 1; n >= 0; n--)
    {
        sprintf(tempString, ",%03i", (long long int) floor((double) inputBytes / pow(1000.0, n)) % 1000);
        memcpy(&output[remn + 4 * (noElements - n - 1)], &tempString[0], 4);
    }
    sprintf(tempString, "%3i", (int) floor((double) inputBytes / pow(1000.0, noElements)) % 1000);
    memcpy(&output[0], &tempString[3 - remn], remn);
    return output;
}