Program to Print Countdown using a While Loop

To create a program that reads a number from the console and prints a countdown from that number to zero, we can use a while loop in the following way:

Step 1: Accepting Input
- We start by accepting the number from the user through the console. This can be done using the input() function in Python, which reads a line of text from the console.

Step 2: Converting Input to Integer
- The input() function returns a string, so we need to convert it to an integer using the int() function. This allows us to perform numerical operations on the input.

Step 3: Initializing a Countdown Variable
- We initialize a variable with the value entered by the user. This variable will be used to control the countdown.

Step 4: Printing the Countdown
- We enter a while loop with a condition that checks if the countdown variable is greater than or equal to zero.
- Inside the while loop, we print the current value of the countdown variable.
- After printing, we decrement the countdown variable by 1.
- This process continues until the countdown variable reaches zero.

Step 5: Exiting the Loop
- Once the countdown reaches zero, the condition in the while loop becomes false, and the loop is exited.
- The program execution continues with the next statement after the while loop, if any.

Example Code:

```python
countdown = int(input("Enter a number: ")) # Step 1 and 2

while countdown >= 0: # Step 4
print(countdown) # Step 4
countdown -= 1 # Step 4

print("Countdown complete!") # Step 5
```

Explanation:
- The above code takes an input from the user and stores it in the variable 'countdown'.
- It then enters a while loop and checks the condition 'countdown >= 0'.
- If the condition is true, it prints the value of 'countdown' and decrements it by 1.
- This process continues until the 'countdown' variable reaches zero.
- Once the countdown is complete, the program exits the while loop and prints "Countdown complete!".

Sample Output:
```
Enter a number: 5
5
4
3
2
1
0
Countdown complete!
```

The program reads an input from the user, initializes a countdown variable, and uses a while loop to print the countdown from the entered number to zero.