Question

Write a C++ statement that prints the message "The number is not valid." if the variable hours is outside the range 0 through 80

Short answer

Question: Write a C++ statement that checks if the variable 'hours' is within the range of 0 to 80 (inclusive). If the value is not in this range, print the message "The number is not valid." Answer: ```cpp if (hours < 0 || hours > 80) { std::cout << "The number is not valid." << std::endl; } ```

Step-by-step solution

Use an if statement to check if 'hours' is outside the range 0 through 80

First, we need to create an if statement that checks if the variable 'hours' is outside the range 0 through 80. To do this, we can use the following condition: (hours < 0) || (hours > 80).

Print out the error message when the condition is true

Inside the if statement, a cout statement should be included to print out the error message. The message should say "The number is not valid."

Complete C++ Statement

Putting the steps together, the complete C++ statement looks like this: ```cpp if (hours < 0 || hours > 80) { std::cout << "The number is not valid." << std::endl; } ```

Key concepts

Understanding 'if' Statements in C++

In computational logic, an 'if' statement is one of the most fundamental concepts for making decisions. C++ 'if' statements check whether a condition is true and execute specific lines of code based on the condition's outcome.

Let's consider a real-world example. If it's raining outside, you decide to take an umbrella. In C++ terms, the condition is 'is it raining?', and the decision is 'take an umbrella'. The 'if' statement in C++ follows a similar pattern. It allows the program to decide whether to perform an action (like printing a message) only when a certain condition is true.

For instance, in the textbook exercise, the program must decide whether to print an error message based on the value of the variable 'hours'. The 'if' statement checks if 'hours' is less than 0 or more than 80, and if this condition holds true, it prints 'The number is not valid.', just like you taking an umbrella if it's raining.

Ensuring Range Validation

Range validation is a crucial technique in programming that ensures data values fall within predefined boundaries or limits. This is akin to setting a minimum and maximum acceptable age for a competition. If an entrant's age doesn't fall within this range, they cannot participate.

In the context of our exercise, the variable 'hours' is expected to be within the range of 0 to 80. To validate this range, the program uses a logical OR operator (||) to combine two conditions: 'hours' being less than 0, and 'hours' being greater than 80.

When 'hours' falls outside of these boundaries, the condition becomes true, prompting the error message to be displayed. Range validation is extremely useful for preventing errors due to unexpected or invalid input, which is a common scenario in real-world applications such as form submissions or user input in software.

Effective Error Handling in C++

Error handling in programming refers to the anticipation, detection, and resolution of programming, application, and communication errors. Good error handling practices help ensure a program behaves gracefully under various unexpected conditions, providing meaningful feedback to users, and allowing for smooth recovery.

In our exercise, error handling is demonstrated by displaying a message when an invalid input is detected. When the condition in the 'if' statement is met (meaning 'hours' is less than 0 or greater than 80), the program responds by outputting 'The number is not valid.'. This is a simple form of error handling where the user is informed of invalid input, and no further action is taken.

In more complex applications, error handling might involve more sophisticated actions such as retrying operations, asking the user for a different input, logging the error for future analysis, or even shutting down processes safely to prevent data corruption.