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);
}