How to counts the number of decimal digits in a positive integer in Python

May 8, 2019 Leave a comment

The following snippet counts the number of decimal digits in a positive integer:

n = 40265
count = 0
while n != 0:
  count = count + 1
  n = n // 10
print(count)

This snippet demonstrates an important pattern of computation called a counter. The variable count is initialized to 0 and then incremented each time the loop body is executed. When the loop exits, count contains the result — the total number of times the loop body was executed, which is the same as the number of digits.

If we wanted to only count digits that are either 0 or 5, adding a conditional before incrementing the counter will do the trick:

n = 2574301453
count = 0
while n > 0:
  digit = n % 10
  if digit == 0 or digit == 5:
   count = count + 1
  n = n // 10
print(count)

The general form of the above program:

n = int(input("Enter the number: "))
this_int = int(input("Enter a positive integer: "))
that_int = int(input("Enter a positive integer: "))
count = 0
while n > 0:
  digit = n % 10
  if digit == this_int or digit == that_int:
    count = count + 1
  n = n // 10
print(count)

By Amit Pratap Singh, India

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