Question

Write an 11 statement that displays the message "The number is not valid" if the variable speed is outside the range 0 through 200 .

Short answer

Question: Write an if statement that checks if a variable "speed" is within the range of 0 to 200 and displays "The number is not valid" if it is not within the range. Answer: ```python speed = 250 # You can replace this value with any other or get the input from the user if speed < 0 or speed > 200: print("The number is not valid") ```

Step-by-step solution

Define the variable speed

First, we need to define the variable "speed" and assign a value to it. For example, you can set it to a given number or get the input from the user.

Check if speed is within the valid range

Now, we need to check if the value of "speed" is within the range from 0 to 200. In Python, we can use an if statement, combined with the logical operator "or" to check two conditions at once. If either of the conditions is true, then the value of "speed" is not within the valid range, and we need to display the message "The number is not valid".

Display the error message if the speed is not valid

If the conditions in the if statement are met (meaning the value of "speed" is outside of the range 0 to 200), we will use the print() function to display the message "The number is not valid". Now, let's see the code in Python. ```python speed = 250 # You can replace this value with any other or get the input from the user if speed < 0 or speed > 200: print("The number is not valid") ```

Key concepts

If Statement

The if statement is a fundamental concept in programming, acting as a decision-making construct that allows a program to execute certain code only when specific conditions are met. In essence, it asks a question and, depending on the answer—true or false—a particular action is taken. For instance:

Imagine a scenario where you want to verify if a person is eligible to vote. The voting eligibility is determined by the person's age being 18 or above. In programming terms, we could write this as:```pythonage = 19if age >= 18: print('You are eligible to vote.')```In a real-world application, such as the exercise on speed range validation, this logic applies similarly. If the condition, or 'question', stated after the if, evaluates to be true, then the program will print out the message indicating that the speed isn't valid. This conditional check is the core of directing a program's flow and is an essential part of programming logic, ensuring that decisions within the program are made rightly and clearly.

Range Validation

Range validation is a procedure where a variable's value is checked to verify whether it falls within a specified range. This is often used to ensure data integrity and to prevent errors in a program's execution. Validating a range can be as simple as checking a number, or as complex as verifying the bounds of a date, a string's length, or an array's size.

In the exercise, the variable speed must fall within the range of 0 to 200. To implement such validation, programmers frequently use comparison operators like less than (<), greater than (>), and logical operators like 'or' and 'and' to define the boundaries of the acceptable range. For example, to check if the value of speed is outside the range, you would write:

```pythonif speed < 0 or speed > 200: # If this condition is true, speed is outside the valid range print('The number is not valid')```If the value of speed does not satisfy the range conditions, a message is displayed to inform the user of the invalid input. It's a crucial part of programming logic to ensure the data you're processing is within the bounds of what the program expects.

Programming Logic

At the core of computer programs lies programming logic, which encompasses the sequence of instructions and the decision-making processes within the code. It operates on algorithms—sets of rules or steps to solve a problem—and logical constructs like loops, conditions, and iterations. Programming logic is designed to orchestrate how a task is executed and to anticipate cases that need special handling.

In the context of the textbook exercise on speed validation, programming logic is used to detect whether the input falls outside an acceptable range and to respond with an appropriate message. The logical structure formed by the if statement and the conditions within serve as a basic example of how logical constructs guide a program's responses. Situations where data needs to be validated or choices made based on certain criteria are where the understanding of programming logic is crucial.

Moreover, a robust grasp of programming logic helps in enhancing code efficiency and readability, preventing unnecessary checks or operations. In more advanced scenarios, it might involve additional layers such as error handling mechanisms and user feedback loops. The underlying aim remains to create a systematic, logical flow that a computer can follow to achieve the desired outcomes efficiently and effectively.