Python Program to Count Digits in a Number

You can count digits in a number in Python by converting it to a string and using len(str(abs(number))) to get the count of digits ignoring the sign.

Examples

Input12345

Output5

Input-987654321

Output9

Input0

Output1

How to Think About It

To count digits in a number, think of the number as a sequence of characters. By converting the number to a string, each digit becomes a character. Then, count how many characters are in that string. Ignore any negative sign by taking the absolute value first.

Algorithm

1

Get the input number.

2

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

3

Convert the absolute number to a string.

4

Count the length of the string to find the number of digits.

5

Return or print the count.

Code

python

number = int(input("Enter a number: "))
digit_count = len(str(abs(number)))
print("Number of digits:", digit_count)

Output

Enter a number: 12345
Number of digits: 5

Dry Run

Let's trace the input 12345 through the code

1

Input number

number = 12345

2

Absolute value

abs(number) = 12345

3

Convert to string

str(abs(number)) = '12345'

4

Count length

len('12345') = 5

5

Print result

Output: Number of digits: 5

Step	Value
Input number	12345
Absolute value	12345
String conversion	'12345'
Length count	5

Why This Works

Step 1: Convert to absolute value

Using abs() removes any negative sign so only digits remain.

Step 2: Convert number to string

Converting to string lets us treat the number as characters to count.

Step 3: Count characters

Using len() on the string gives the total number of digits.

Alternative Approaches

Using a loop and integer division

python

number = int(input("Enter a number: "))
count = 0
num = abs(number)
if num == 0:
    count = 1
else:
    while num > 0:
        num //= 10
        count += 1
print("Number of digits:", count)

This method counts digits by dividing the number repeatedly by 10. It avoids string conversion but is longer.

Using math.log10

python

import math
number = int(input("Enter a number: "))
num = abs(number)
if num == 0:
    count = 1
else:
    count = int(math.log10(num)) + 1
print("Number of digits:", count)

This uses logarithms to find digit count efficiently but requires importing math and careful handling of zero.

Complexity: O(n) time, O(n) space

Time Complexity

Converting the number to a string takes time proportional to the number of digits, so it is O(n).

Space Complexity

The string conversion requires extra space proportional to the number of digits, so O(n).

Which Approach is Fastest?

The string method is simple and fast for typical use. The loop method is slower but uses constant space. The math.log10 method is fastest but needs careful zero handling.

Approach	Time	Space	Best For
String conversion	O(n)	O(n)	Simplicity and readability
Loop with division	O(n)	O(1)	Memory efficiency without strings
Math log10	O(1)	O(1)	Performance with numeric math