C# Program to Count Digits in a Number

You can count digits in a number in C# by converting it to a string and using number.ToString().Length or by repeatedly dividing the number by 10 and counting the steps with a loop.

Examples

Input12345

Output5

Input0

Output1

Input-9876

Output4

How to Think About It

To count digits in a number, think about how many times you can divide the number by 10 before it becomes zero. Each division removes the last digit, so counting these divisions tells you how many digits the number has. For negative numbers, ignore the sign and count digits of the absolute value.

Algorithm

1

Get the input number.

2

Convert the number to its absolute value to ignore negative sign.

3

If the number is zero, return 1 because zero has one digit.

4

Initialize a count variable to zero.

5

While the number is greater than zero, divide it by 10 and increment the count.

6

Return the count as the number of digits.

Code

csharp

using System;
class Program {
    static void Main() {
        int number = -9876;
        int count = CountDigits(number);
        Console.WriteLine(count);
    }
    static int CountDigits(int num) {
        num = Math.Abs(num);
        if (num == 0) return 1;
        int count = 0;
        while (num > 0) {
            num /= 10;
            count++;
        }
        return count;
    }
}

Output

4

Dry Run

Let's trace the number -9876 through the code to count its digits.

1

Start with number

Input number = -9876

2

Convert to absolute

num = 9876

3

Check if zero

num != 0, continue

4

Initialize count

count = 0

5

Loop divide and count

num=9876, count=0 -> num=987, count=1 -> num=98, count=2 -> num=9, count=3 -> num=0, count=4

6

Return count

count = 4

num	count
9876	0
987	1
98	2
9	3
0	4

Why This Works

Step 1: Handle negative numbers

Using Math.Abs removes the negative sign so digit count is correct.

Step 2: Count digits by division

Dividing by 10 removes the last digit each time, so counting divisions counts digits.

Step 3: Special case zero

Zero has one digit, so return 1 immediately if input is zero.

Alternative Approaches

String conversion

csharp

using System;
class Program {
    static void Main() {
        int number = 12345;
        int count = number.ToString().TrimStart('-').Length;
        Console.WriteLine(count);
    }
}

This method is simple and uses string length but may be slower for very large numbers.

Recursive division

csharp

using System;
class Program {
    static void Main() {
        int number = 4567;
        Console.WriteLine(CountDigits(number));
    }
    static int CountDigits(int num) {
        num = Math.Abs(num);
        if (num < 10) return 1;
        return 1 + CountDigits(num / 10);
    }
}

This uses recursion to count digits but can cause stack overflow for very large numbers.

Complexity: O(d) time, O(1) space

Time Complexity

The loop divides the number by 10 each time, so it runs once per digit, making it O(d) where d is number of digits.

Space Complexity

Only a few variables are used, so space is constant O(1).

Which Approach is Fastest?

The division loop is efficient and uses constant space; string conversion is simpler but may use more memory.

Approach	Time	Space	Best For
Division loop	O(d)	O(1)	Efficient for all integer sizes
String conversion	O(d)	O(d)	Simple code, good for small to medium numbers
Recursive division	O(d)	O(d)	Educational, but risky for large numbers