repetitions

i want to find combination of elements in an array with two rules : 1. the output should be 4 (for 4 arr elements) 2. repetitions are allowed eg {A,B,C,D} o/p: {A,A,A,A} {A,A,A,B} {A,A,B,B} '' '' '' thanx in advance.. (coding in c#/c)