How can I find the number 9s in an integer

Question

I have the following method, which was to find the total number 9 in integers, the method is used to get the contract type of employees based on the number 9. I tried the following class: -

public class EmployeeCreditCards { public uint CardNumber(uint i) { byte[] toByte = BitConverter.GetBytes(i); uint number = 0; for (int n = 0; n < toByte.Length; n++) { if (toByte[i] == 9) { number = number + 1; } } return number; } } 

In which I am trying to find how many 9 are in the passed integer, but the above method will always return zero. Any idea what is going wrong?

Answer 1

You can do it simply with a little linq:

 public int GetAmountOfNine(int i) { return i.ToString().Count(c => c.Equals('9')); } 

But add using System.Linq; to the cs file.

Your answer does not work, because you convert to bytes, converting a number to bytes does not generate a byte for each digit _{(via @Servy ) sub>. Therefore, if you write each byte in your array for the / debug console, you will not see your number back.}

Example:

 int number = 1337; byte[] bytes = BitConverter.GetBytes(number); foreach (var b in bytes) { Console.Write(b); } 

Console:

57500

However, you can convert int to string and then check each character in the string if it is nine;

 public int GetAmountOfNineWithOutLinq(int i) { var iStr = i.ToString(); var numberOfNines = 0; foreach(var c in iStr) { if(c == '9') numberOfNines++; } return numberOfNines; } 

Answer 2

The classic solution is as follows: (This is probably the fastest algorithm to find a solution, only O (log n) is required.)

 private int count9(int n) { int ret = 0; if (n < 0) n = -n; while (n > 0) { if (n % 10 == 9) ++ret; n /= 10; // divide the number by 10 (delete the most right digit) } return ret; } 

How it works? Consider an example, n = 9943

now ret = 0.

n% 10 = 3, which! = 9

n = n / 10 = 994

n% 10 = 4! = 9

n = 99

n% 10 = 9, so ret = 1

n = 9

n% 10 = 9, so ret = 2

n = 0

Answer 3

Try

 int numberOfNines = number.ToString().Where(c => c == '9').Count(); 

Since a string implements an IEnumerable<char> , you can apply LINQ directly to a string without first converting it to an enumeration of characters.

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UPDATE

Converting uint to an array of bytes will not work as expected, since uint does not store the decimal digits of your number directly. The number is stored as a binary number, which is incremented by four bytes. A unit always has four bytes, even if your number has 9 decimal digits.

You can convert a number to a string to get its decimal representation.