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Nov 4th, 2008

Recursive Function to Reverse an Integer

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I have an assignment to write a recursive function that takes one integer variable and output the integer in reverse order to the screen. I've tried converting it to a char array(c++ "string" class not allowed) but could not get a counter to work. I can reverse an int array with and "upper" and "lower" variable no problem, but I'm stuck without them.

???? reverse(int num) //This is what the assignment calls for.

I'm not looking for anyone to write it for me but I would appreciate some tips.
Thanks in advance.

badmofo

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Nov 4th, 2008

Re: Recursive Function to Reverse an Integer

Why would you need to use a char array? using int array should be fine.

(Toggle Plain Text)

reverse (num)
   array[count] = num
   count ++
   get a new num
   reverse (num)
   print out array[count]
   count--

It might be logically flawed somewhere..just make sure you have a base case (where you would stop calling the reverse function).

Last edited by freudian_slip; Nov 4th, 2008 at 12:54 am.

freudian_slip

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Nov 4th, 2008

Re: Recursive Function to Reverse an Integer

If you're just displaying the reversed thing to the screen, there is no need to store any numbers in any arrays.

Each call to the function will print out a single digit (the digit of number in the units place). If the number is more than 9, the function will call itself with number/10 as the argument. This will recursively print out the number in reverse. When all digits have been printed, the function will stop, and return, due to the above stated call condition.

dougy83

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Nov 4th, 2008

Re: Recursive Function to Reverse an Integer

raw scetch of how I should start to do it:
revprint(int n)
{
if n==0 return
cout<<n%10
revprint(n/10)
}

ddanbe

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Nov 4th, 2008

Re: Recursive Function to Reverse an Integer

I'd do it that way too, just I'd add a little if-else-abs() trick to handle n<0 (otherwise it would print -567 reversed as -7-6-5).

something like

C++ Syntax (Toggle Plain Text)
if(n<0) {
     cout << "-" << abs(n%10);
     revprint(n/-10);
}
else {
     cout << n%10;
     revprint(n/10);
}
if(n<0) {
     cout << "-" << abs(n%10);
     revprint(n/-10);
}
else {
     cout << n%10;
     revprint(n/10);
}

Last edited by mrboolf; Nov 4th, 2008 at 10:32 am.

mrboolf

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Nov 5th, 2008

Re: Recursive Function to Reverse an Integer

Thanks everyone! I got it working using "n % 10" I was making it too complicated as usual

badmofo

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Nov 5th, 2008

Re: Recursive Function to Reverse an Integer

So you can mark this as solved.

ddanbe

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Sep 24th, 2010

Re: Recursive Function to Reverse an Integer

if we give a input which has a digit 0 in between it then loop will end there and output will be incorrect
for eg 1034
the loop will end at the second digit 0 and otput will be incorrect

what to do in this case??

anuj khasgi

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