Thread: Recursion binary to decimal - question.

Hi,
I was asked to program a recursion (in C), which converts a binary to decimal.
The below code works well, yet I am not sure it fully exploits the potential of recursion (in particular the first two lines):

Code:

int convert_bin_to_dec(int num)
{
    iter++;
    if (iter != 1) count*=2;
    if (!(num / 10)) return (num * count);
    return ((num % 10) * count + convert_bin_to_dec(num /10));
}

Iter and count are global variables set to 0 and 1 respectively.
I'd sincerely appreciate any feedback/suggestions.

Why are global variables considered wrong in this case? We weren't explicitly forbidden to make use of global variables. How would you advise approaching it otherwise? The input of the binary number is in main(). Would you need that to assist me? I'd gladly post it if needed.

You didn't really elaborate how it ought to be handled differently. Would you recommend using another function to yield the number of binary digits the input has?

A helper function would allow you to set up iter and count inside and not have them as globals.

How about this?

Code:

int convert_bin_to_dec(int num)
{
    if (!(num / 10)) return (num);
    return (num % 10 + convert_bin_to_dec(num / 10) * 2); 
}

Is this valid?

I do not think the code you pasted now accounts for place value:

For example

2^0 2^1 2^2 2^3 2^4
1 0 1 0 1

which is 21.

It's a specific multiplication you need to perform in each place.

But it works perfectly! You may run it and see for yourself.

And with your input (viz. 10101) 21 was indeed the answer the program yielded.

It does! (As I have verified)

If you have no further remarks or comments to make, I would like to thank you sincerely for your kind assistance!

I'd appreciate your comments on the following recursion, confirming that the number is a binary number (defined to be a positive number of 0's and 1's). Note, I am not allowed to use arrays, strings, pointers. We were instructed to use recursion!

Code:

int is_valid_bin_num(int num)
{
    if (num / 10 > 0 && num % 10 <= 1) return (is_valid_bin_num (num / 10));
    if (num == 1 || num == 0) return 1;
    return 0;
}

It feels slightly cumbersome to me.