Nice code, Few things

1) You used GOTO, avoid using GOTO, whether its for college or otherwise (in fact specially for college as your teachers will blast at you no matter what the reason is, do not use GOTO. One of my friend used this in the test, he Got 20/50 just because he used GOTO otherwise his code was good to get above 35 atleast...So you can imagine.)

"I have found his all important line mssing in many standard books "
English mistakes (ask any mod to correct it if you can't, and second instead of saying that say why you added it, I haven't seen the code but it would be nice if you give some brief account of what the line/function is about wherever necessary and what the variables are for so the idea of the code is more clear to the newbies.
Also instead of saying
"The Line I added in the code from standard code makes it more efficient for longer arrays"
Say, by adding this the code gets efficient in this way, and If i don't use this line this is what happens. This will not only make us appreciate about it, newbies will understand your code more easily...

 cout<<a[k]<<" ";
Since you didn't use { } the, for loop is only for first cout, but the identation may confuse the newbies, as selection sort is one of the basics, This thread will be checked by people who are newbies in C++. Thus from that idea, make things more clearer so that they don't get confused about it..

Nice effort...Post more..