Question

Write an input statement validation loop that prompts the user to enter a number less than 20 or greater than 75.

Short answer

Use a loop with conditions `num < 20 or num > 75` and handle non-integer inputs with a try-except block.

Step-by-step solution

Understand the Problem

We need to write a loop that continuously asks the user for input until they provide a valid number. The number must be either less than 20 or greater than 75.

Determine Loop Logic

We will use a `while` loop that continues to prompt the user for input as long as the entered number is between 20 and 75, inclusive. Thus, the valid input is any number `x` for which the condition either `x < 20` or `x > 75` holds true.

Construct the Input Statement

We use `input()` in Python to get user input. Since `input()` returns a string, we'll convert this to an integer using `int()` before validating the number. We'll also implement basic error handling for non-integer inputs.

Implement the Validation Loop

The validation loop can be set up as follows: ```python while True: try: num = int(input("Enter a number less than 20 or greater than 75: ")) if num < 20 or num > 75: print("Valid number entered.") break else: print("Invalid input, try again.") except ValueError: print("Please enter a valid integer.") ```

Test the Code

After writing the loop, test it with different inputs like `10`, `30`, `80`, and non-integer inputs to ensure it only breaks when a valid number is entered and handles errors correctly.

Key concepts

While Loop

While loops are fundamental constructs in programming that repeatedly execute a block of code as long as a specified condition is true. They are particularly useful when the number of iterations is not known beforehand.
In our context, the `while` loop keeps asking the user to input a number until they enter a valid one (either less than 20 or greater than 75). The loop condition in this exercise is essentially an infinite loop with a `True` condition, allowing it to continue running until a `break` statement intervenes upon satisfying the input condition. This makes the while loop uniquely suited for this type of validation task, where the requisite ending is reliant on user action rather than a set number of iterations.
Using a `while` loop, you can easily control the flow of the program based on dynamic conditions, such as user input, ensuring that the program behaves predictably and meets the specific requirements outlined in a problem.

Conditional Statements

Conditional statements are logic building blocks in programming, allowing code to make decisions based on certain conditions.
In our exercise, we apply the `if-else` conditional statements within a loop to discern whether the input meets the criteria (less than 20 or greater than 75). If the input number fulfills the condition, the script acknowledges the validity and exits the loop using the `break` statement.
Otherwise, an `else` clause prompts the user to try again until a valid input is provided. This structure provides the straightforward logic to guide the user's interaction with the program, ensuring errors or invalid entries lead the user back to correct their input.

Error Handling

Error handling is crucial in programming to ensure robustness and user-friendly experiences. It involves anticipating potential errors in a program and providing solutions to handle these instances gracefully.
In this exercise, error handling plays a vital role in managing non-integer inputs. A `try-except` block captures exceptions—like when a user inputs letters instead of numbers. If a `ValueError` occurs (which happens with non-integer inputs), a user-friendly message prompts them to provide a valid integer, thus maintaining smooth program execution.
This method not only helps in preventing the program from crashing but also enhances user experience, making sure they understand the nature of their input error and how to correct it effectively.

User Input

User input is critical in interactive programs where the user's decisions control the flow of execution.
Using the `input()` function in Python, our program queries the user for a specific number. Since `input()` returns a string by default, we convert it into an integer with `int()` to evaluate its numerical value against the required conditions.
Collecting user input makes the program dynamic, reacting in real-time to external data provided at each run loop. In applications, this is key to making your program useful and interactive, setting a responsive environment where user actions dictate the operational context of the software.