Help on permutation and combination.

[Devung]

Need coding for a program where given positive integers n and r, to find the number of r-permutations when repetition is allowed and r-combinations when repetition is allowed of the ser with n-element. the program should accept user's input and list down the r-permutations and r-combinations in lexicographic order.
...really desperate for help..thanks!

[D_C]

Some formulas may help.

nPr or P(n,r) = n! / (n-r)!

nCr or C(n,r) = n! / r!(n-r)!

In other words, (nCr * r!) = nPr.