while loop

using System;

public static class CollatzConjecture
{
    public static int Steps(int number)
    {
        if (number <= 0)
            throw new ArgumentOutOfRangeException(nameof(number));

        var currentNumber = number;
        var stepCount = 0;

        while (currentNumber != 1)
        {
            if (currentNumber % 2 == 0)
                currentNumber = currentNumber / 2;
            else
                currentNumber = currentNumber * 3 + 1;

            stepCount++;
        }

        return stepCount;
    }
}

The first step is to check the number parameter for validity:

if (number <= 0)
    throw new ArgumentOutOfRangeException(nameof(number));

We then define two variables:

• currentNumber: contains the current number in the sequence as a result of repeated application of the algorithm (with its starting value being the number parameter)
• stepCount: keeps track of the number of steps (which is the number of times we apply the algorithm)

var currentNumber = number;
var stepCount = 0;

Then a while loop starts by checking whether the current number is not equal to 1; if it is, the method terminates:

while (currentNumber != 1)

Within the loop, we update the currentNumber based on the algorithm, re-assigning its value with its next value in the sequence.

if (currentNumber % 2 == 0)
    currentNumber = currentNumber / 2;
else
    currentNumber = currentNumber * 3 + 1;

Then we increment the number of steps, to indicate that we've just applied the algorithm:

stepCount++;

The while loop then continues until the currentNumber is equal to 1, after which we return the step count:

return stepCount;

Shortening

A ternary operator can be used instead of an if statement:

currentNumber = currentNumber % 2 == 0 ? currentNumber / 2 : currentNumber * 3 + 1;