# Sorting a list of zeros and ones.

1. Jul 8, 2007

### MathematicalPhysicist

Assume i have an initial list of n-2 columns and 2^(n-2) rows, where initially:
all the entries are zero.
i wnt to sort it out that eveantually we'll get a truth table for this.
i.e if we have n-2=2 rows and 4 columns, then:
Code (Text):

0 0
1 0
0 1
1 1

obvously we have here a jump first we initialise the array to give us everywhere zero, afterwards i need to insert via a loop the entries of 1, i.e in the first column it should be changing the zeros in a[1][1] and a[3][1] i.e we have a jump of two places and in the next column a jump of three places, but i don't know how to write it in the loop condition, any thoughts?
the exam is tommorow, so your help would be tremendous for my success, thanks in advance.

2. Jul 8, 2007

### -Job-

You mean you want to generate something like this:
Code (Text):

... 0 0 0 0
... 0 0 0 1
... 0 0 1 0
... 0 0 1 1
... 0 1 0 0
... 0 1 0 1
... 0 1 1 0
... 0 1 1 1
... 1 0 0 0
... 1 0 0 1
... 1 0 1 0
... 1 0 1 1
... 1 1 0 0
... 1 1 0 1
... 1 1 1 0
... 1 1 1 1
... . . . .
. . . .
. . . .

?

3. Jul 8, 2007

### chroot

Staff Emeritus
Is there some particular reason you need to do this with nested for loops and complicated conditions? There are many simpler approaches.

- Warren

4. Jul 13, 2007

### MathematicalPhysicist

yes job, something like that.

chroot, iv'e learned loops, so i guess this is the way i shouldv'e solved it.

thanks anyway.

5. Jul 13, 2007

### chroot

Staff Emeritus
If I were doing it, I'd just use a single for loop that increments a counter. To extract each bit from the counter, I'd use a set of masks, one for each bit.

- Warren