How to reverse a number?

Hi,

I want to reverse a number without using MATLAB functions "digitrevorder()" and "fliplr()". Please help. Thank you!

Answer 1

[Evan]

x = 1234;
s = num2str(x) - '0';
xr = polyval(s(end:-1:1),10)

[Evan]

Note that this answer is for a single number (scalar), not a vector.

[John D'Errico]

+1

I suppose polyval works here, though I would not have approached it that way.

You could as easily have just used str2num, in which case polyval would be unnecessary, as well as the conversion from char to numeric in the middle by subtracting '0'.

A = 1234;
B = num2str(A);
B = str2num(B(end:-1:1))
B =
        4321

There are often many ways to solve a problem in MATLAB, all of which are quite reasonable.

[Evan]

Doh! I don't know what I was thinking! That's a much less convoluted way. I'm so used to having to use the polyval trick for CODY problems that I didn't even think about that. Thanks!

[Image Analyst]

For what it's worth, I was thinking of John's method too (which he should have put as a separate answer so I could vote for it.)

[Guillaume]

I would think that since it looks very much like an assignment, the idea is to force the student to use a loop. There's certainly no point of disallowing fliplr if you allow any of the solutions presented here.

[John D'Errico]

A moderately interesting question is to find a solution in one line, without needing to form an intermediate variable. (And without the application of fliplr!) Seems trivial with that function.

[Guillaume]

You also want to disallow rot90, flipud and flip, otherwise it's also trivial.

Answer 2

[Syed Haider]

A = [1 2 3 4; 5 6 7 8];
y = A(:,end:-1:1)

[John D'Errico]

That reverses a vector or array of numbers, not the digits of a single number.

[Syed Haider]

Yeah you are right :) I am sorry. Should i remove the answer? or may be it will be helpful for someone.

[John D'Errico]

I don't see any reason to remove it.