Write method that checks if a given number (positive integer) contains digit 3. If it is true answer is true.if it is false answer is false.in C#

Question

Do not convert number to other type. Do not use built-in functions like Contains() , StartsWith() , etc.

while (number > 0)
{
      if (number % 10 == 3)
      {  
          return true;
      }
      number /= 10;
  }
 return false;` 

Answer 1

Method that checks if given number (positive integer) contains digit 3

You were nearly there

private static bool HasDigit(int num,int digit)
{
   while (num > 0)
   {
      if(num % 10 == digit)
         return true;
      num /= 10;
   }
   return false;
}

Usage

Console.WriteLine(HasDigit(1222, 3));
Console.WriteLine(HasDigit(23345, 3));

Output

False
True

Other approaches might be

private static bool HasDigit2(int num, int digit)
{
   var str = num.ToString();
   for (int i = 0; i < str.Length; i++)
      if (str[i] == ((char) digit) + '0')
         return true;
   return false;
}

Or

private static bool HasDigit3(int num, int digit)
   => num.ToString().Any(t => t == ((char) digit) + '0');

Answer 2

Here's a recursive solution:

public static bool Contains3(int n) {
            if (n < 10) {
                if (n == 3) {
                    return true;
                } else {
                    return false;
                }
            }
            return n % 10 == 3 || Contains3(n / 10);
        }