find al subsets

hello to everybody.
i try to create an algorithm tha for any number [0,26] find all the subset of the alphabet.
for example if you give to the programm the number 4 the programm print out

{}
{a}
{b}
{a,b}
{c}
{a,c}
{b,c}
{a,b,c}
{d}
{a,d}
{b,d}
{a,b,d}
{c,d}
{a,c,d}
{b,c,d}
{a,b,c,d}

i have been thinking something.i would like to hear any ideas.
thanks for any reply

 

i saw this thread.it is very interesting.i open this thread for more ideas.
thanks anyway

 

You can make use of next_permutations

 

Ah, yes. Thanks for correction.

 

thanks a lot guys