C implementation of an algorithm for generating k-subsets of an n-set in lexicographic order (with respect to indexes). There is also TeX source of an unfinished note describing the algorithm.
Compile with gcc subs.c -o subs.
Calling ./subs 5 3 generates all 3-subsets of {1,2,3,4,5} in lexicographic order:
blazs@blazs-laptop:~/Documents$ ./subs 5 3
1 2 3
1 2 4
1 2 5
1 3 4
1 3 5
1 4 5
2 3 4
2 3 5
2 4 5
3 4 5