Should have tested, dest++...d'oh! And brackets not necessary for *src++. This works, copying the string in just one line; that's why I couldn't believe the OP couldn't figure this out on the day before his exam; it must have been a really crappy programming course if it left people unable to work out a simple strcpy.
Code:
void go4e_38959()
{
char a[32];
char b[32];
char *pa;
char *pb;
strcpy(a,"Hello world");
pa=a;
pb=b;
while (*pb++=*pa++) ; // <- just bung this line in a function to meet the requirement
printf("%s\n",b);
}