while(*s++=*t++);
Guess what it it does? It copies a string. It actually meant this.
while (*t != 0) {
*s = *t;
s++;
t++;
}
Basically the process goes as follows, the contents of t (*t) are copied to s (*s) at every loop. Both s and t are then incremented with (++). And when (*t) couldn't get any further, it breaks out of the while loop. A string is then copied through that one lines of code, while being written in a much more compacted way.