How to generate MAC address automatically by C language

Recently, when I was working on the virtual machine project, I needed to automatically generate a MAC address for each virtual machine created. Since the MAC address is 48 bits and the format is: separated, I wrote a c program to automatically generate the MAC address.

//   MAC.c
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<unistd.h>
#define RANDOM(x) (rand()%x)
#define MAC_ADDR_LENGTH 12
#define FMT_MAC_ADDR_LEN (MAC_ADDR_LENGTH+5)
unsigned char HEXCHAR[16]={'0','1','2','3','4','5','6','7','8','9','A','B','C',
'D','E','F'};
unsigned char genMACAddr[MAC_ADDR_LENGTH];
unsigned char fmtMACAddr[FMT_MAC_ADDR_LEN]={'0','0','-','0','0','-','0','0','-',
'0','0','-','0','0','-','0','0'};
void formatMACAddr()
{
  unsigned short i=0;
  unsigned short n=0;
  for(i=0;i<MAC_ADDR_LENGTH;i++,n++)
  {
    if(fmtMACAddr[n]!='-')
    {
      fmtMACAddr[n]=genMACAddr[i];
    } 
    else
    {
      n++;
      fmtMACAddr[n]=genMACAddr[i];
    }
  }
}
void main()
{
  unsigned short i=0;
  unsigned short n=0;
  srand(getpid());
  for(int i=0;i<MAC_ADDR_LENGTH;i++)
  {
    n=RANDOM(16);
    genMACAddr[i]=HEXCHAR[n];
  }
  formatMACAddr();
  printf("%s",fmtMACAddr);
}