Question

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

Short answer

Question: Write an if statement to check if the variable "speed" is outside the range of 0 to 200 and display the message "The number is not valid" if it is. Answer: ```python if speed < 0 or speed > 200: print("The number is not valid") ```

Step-by-step solution

Understanding the condition

First, analyze the condition: "The number is not valid" should be displayed if the value referenced by speed is outside the range of 0 to 200. This means that if speed is less than 0 or greater than 200, the message should be displayed.

Writing the if statement

Write the if statement to check if the value of speed is less than 0 or greater than 200. If the condition is met, it will print the message "The number is not valid". ```python if speed < 0 or speed > 200: print("The number is not valid") ``` This will ensure that the message is only displayed when the value of speed is outside the specified range of 0 to 200.

Key concepts

Conditional Statements

Conditional statements in Python are a fundamental aspect of making decisions within your code. They allow you to run certain code blocks only if specified conditions are met.
A basic form of a conditional statement is the `if` statement. This determines whether a block of code will run, depending on whether the expression evaluated returns `True`.
Consider the example: ```python if condition: # code to execute if condition is true ``` Here, the `condition` is an expression that Python evaluates. If it's true, the indented code block runs. This pattern is essential in scenarios where different outcomes are expected based on varying conditions, like checking if a number lies within a specific range.

Control Structures

Control structures are constructs which give developers the ability to build more complex and efficient code flows. In Python, the primary control structures include conditional statements, loops, and functions.
For our exercise, `if` statements serve as both a control structure and a conditional check. They select the flow of execution based on the outcome of certain conditions.
Using an `if` statement in conjunction with logical operators (such as `or`, `and`, `not`), you can construct highly precise decision-making processes. The code below checks two conditions with an `or` operator, which helps in range-checking: ```python if speed < 0 or speed > 200: print("The number is not valid") ``` Here, control is handed to the print statement if either condition is true, demonstrating how multiple pathways in the control structure are evaluated.

Range Checking

Range checking involves verifying if a number falls within a specific interval. It is common in programming when validating input or ensuring the program's context remains accurate.
The original exercise checks whether `speed` is outside the valid range of 0 to 200 using two conditions: `speed < 0` and `speed > 200`. Either condition being true implies that `speed` is not within the permissible range. A simple and effective way to perform this check in Python involves utilizing the `if` statement and logical operators. The code used in the solution exemplifies this: ```python if speed < 0 or speed > 200: print("The number is not valid") ``` Understanding how range checks work allows developers to set firm boundaries for variable values, crucial for data integrity and bug prevention.