CODEWITHSUNDEEP
c++mathdigits
Itban Saeed
Itban Saeed

Reputation: 1666

C++: finding a specific digit in a number

Someone please guide me how to check whether a specific digit exists in an integer or not. for the sake of code optimization I am trying to avoid the use of strings or any kind of loops to iterate over all the digits of the integer.

If I need to find out whether 4 exists the in an integer or not, input and the output samples are given below:

Sample Input:

154

Sample Output:

true

Desired Code:

bool ifExists(int digit, int number)
{
    if()
    {
        return true;
    }
    else
    {
        return false;
    }
}

Possible Logic:

I believe there must be a mathematical approach which will do the job in the if condition, however I am unable to find such method in cmath library.

Upvotes: 0

Views: 825

Answers (2)

Oelsni
Oelsni

Reputation: 1

A mathematical approach would be possible i think. By using log(x) in some crazy way.

But ones for surey you should use string or a loop by dividing by 10. log(x) requires far more resources than the way you want to use.

Also string or dividing by 10 is far more easy to read than a mathimatical solution.

For the mathimatical solution.

I suggest you try to transform the decimal number in a binary representation of it. Then it could be possible to create a filter for the digit you look for. By joining the filter and the transformed value through a bitwise & you could get what you seek. Im not sure if that realy is possible but that would be my first idea for an approach.

But as i said before. This method will be very expensive to the cpu and will be hard to read.

Upvotes: 0

Lutz Lehmann
Lutz Lehmann

Reputation: 25972

Convert integer to string, do a string search for digit.

The "mathematical" method would have to do the same, compute the digit sequence by division/remainder by 10 and compare with the given digit.

Upvotes: 4

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