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 0 through 80, and if it's not, prints a 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

Initialize variable "hours" with some value

First, you need to declare and initialize an integer variable "hours" to some value, which will be later checked if it is within the valid range. Here is an example of how you can do it: ```cpp int hours = 50; // This value can be any number that represents the number of hours. ```

Use if statement and comparison operators to check the range

Next, you need to implement an if statement to check if the "hours" variable is outside the range 0 through 80. To do that, you can use comparison operators such as "greater than" (>) or "less than" (<) and logical operator "OR" (||). Here's how you can check if "hours" is outside the valid range: ```cpp if ( hours < 0 || hours > 80) { ```

Print the message if "hours" is outside the valid range

Since the conditions in Step 2 check if "hours" is outside the valid range, you can now print a message "The number is not valid." within this if statement: ```cpp std::cout << "The number is not valid." << std::endl; ``` To complete the if statement, you must close the braces: ```cpp } ```

Final code

Combining all the steps, the final C++ code should look like this: ```cpp #include int main() { int hours = 50; // This value can be any number that represents the number of hours. // Check if hours is outside the range 0 through 80 if ( hours < 0 || hours > 80) { std::cout << "The number is not valid." << std::endl; } return 0; } ```

Key concepts

Comparison Operators

In C++, comparison operators are essential tools for making decisions within a program. They allow you to compare two values or expressions. In the given exercise, comparison operators are used to check whether a variable falls within a specified range.

• Less Than (<): Checks if the value on the left is smaller than the value on the right. For instance, in the expression `hours < 0`, we are verifying if the variable `hours` has a value less than 0.
• Greater Than (>): Checks if the value on the left is larger than the value on the right. In the expression `hours > 80`, we are checking whether the `hours` variable exceeds 80.

By combining these operators, you can form complex conditions that help decide the flow of the program. In the exercise, these operators are used together with logical operators to ensure that the value of `hours` is valid. Understanding how these operators work is crucial when dealing with ranges and conditions in C++ programming.

Logical Operators

Logical operators in C++ are used to create complex conditional checks by combining multiple comparison operations. In the context of the exercise, logical operators play a key role in making sure that a value either fits within certain conditions or doesn't.

• Logical OR (||): This operator checks if at least one of the conditions is true. In the statement `hours < 0 || hours > 80`, the OR operator is used to determine if the `hours` variable is either less than 0 or greater than 80.
• When using logical operators, remember that they evaluate from left to right. However, if one condition proves true, the remaining conditions do not need to be evaluated, saving computational time.

Understanding logical operators is fundamental when you want to check for conditions where more than one possibility can result in the same action (such as printing "The number is not valid."). They are essential for coding robust C++ programs where complex logic needs to be evaluated.

Variable Initialization

Before you can use a variable in C++, it must be declared and initialized. Initialization is the process of assigning a starting value to a variable, ensuring that it holds a known value before it is used in any operations.
In the exercise, the `hours` variable is initialized as follows: ```cpp int hours = 50; ```

• This line declares a variable of type `int`, which stores an integer value. It's crucial to initialize variables to avoid undefined behaviors that can cause unpredictable results in your program.
• Choosing an appropriate initial value is important, especially if the variable will later be checked against certain conditions. In this case, `hours` can be any integer that potentially represents hours worked or logged.

A well-initialized variable forms the foundation for reliable and effective code execution. When variables are correctly initialized, it guarantees that comparison and logical operations using this variable are based on accurate data.