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 to repeatedly ask for input until it's <20 or >75.

Step-by-step solution

Initialize Variables

Start by initializing any variables you might need for the loop. For this exercise, you will need a variable to store the user's input.

Set up the Loop

Create a loop that will continue to execute until the input condition is satisfied. In this case, the input must be less than 20 or greater than 75.

Prompt the User for Input

Inside the loop, use an input statement to ask the user to enter a number. This input should then be converted to a numeric data type if necessary.

Validate User Input

Check if the user's input meets the required condition, i.e., less than 20 or greater than 75. This involves using a conditional statement (like an 'if' or 'while') to compare the input with 20 and 75.

Exit the Loop if Valid

If the user's input satisfies the condition (less than 20 or greater than 75), allow the loop to terminate. Otherwise, prompt them again for a correct input.

Key concepts

Understanding Loop Structures

In programming, loops are a fundamental concept that allow us to repeat a block of code multiple times. This repetition is controlled by a condition.
A loop will continue to execute until the condition is no longer satisfied. There are several types of loops. The most common are:

• while loops: These execute as long as a specified condition is true.
• for loops: These iterate over a sequence or continue for a specific number of iterations.

For this exercise, a "while loop" is most suitable. This is because we do not know how many attempts the user will need to input a valid number. The loop will ask for input and check conditions until the number is valid. The process of repeatedly checking the condition is integral to input validation.

Using Conditional Statements

Conditional statements are used to decide which block of code should be executed based on certain conditions. They provide the logical decision-making ability in code, allowing it to react differently according to various inputs.
The main types of conditional statements are:

• if: Executes a block of code if its condition is true.
• else: Follows an "if" statement and executes if the preceding "if" condition is false.
• elif (or "else if"): Checks another condition if the previous conditions are false.

In the given problem, we use these statements to determine if a user's input is valid. For this exercise, we might want to use an "if" statement within our loop to check if the number is less than 20 or greater than 75. If true, the loop can end.

Handling User Input

Receiving input from users is a basic and essential part of interactive programs. User input allows the program to behave in a dynamic and personalized manner rather than following a fixed path.
Here's how to effectively handle user input:

• Use input functions to capture data entered by the user. Functions like `input()` in Python are designed for this purpose.
• Convert the input if necessary. Since user input is often received as text (string), you might need to convert it to a number using functions like `int()` or `float()`.

In our exercise, we ask the user for a number and convert it to a numeric type immediately to ensure we can perform numerical checks needed for validation.

Ensuring Number Validation

Number validation is ensuring the input meets predetermined numerical conditions or constraints. This can enhance the robustness and reliability of a program. Here are key points for validating a number:

• Check if the number falls within a specified range or matches set conditions.
• Inform the user when input is invalid and prompt to re-enter.

In our exercise, the key challenge is validating that the number is either less than 20 or greater than 75. The input loop continues to prompt the user until a valid number conforms to these conditions. Proper validation prevents incorrect processing and enhances user experience by ensuring their inputs are correct before proceeding.