how random privkey vanitygen modification

[directoryio]

Hello I don't usually program in C so I have a big problem:
here is a code portion that allows vanitygen to start searching patterns from a specific private key

  privkey[0]=0;
  privkey[1]=0;
  privkey[2]=0;
  privkey[3]=be64(2);

which gives 0000000000000000 for privkey[0]=0
                    0000000000000000 for privkey[1]=0
                    0000000000000000 for privkey[2]=0
                    0000000000000003 for privkey[3]=be64(2)

either 00000000000000000000000000000000000000000000000000000000000000000003

how to make privkey[3]=be64(2) RANDOM? in C

thanks.