Question

The cost of sending a package by an express delivery service is \(\$ 10.00\) for the first two pounds, and \(\$ 3.75\) for cach pound or fraction thereof over two pounds. If the package weighs more than 70 pounds, a \(\$ 10.00\) excess weight surcharge is added to the cost. No package over 100 pounds will be accepted. Write a program that accepts the weight of a package in pounds and computes the cost of mailing the package. Be sure to handle the case of overweight packages.

Short answer

To calculate the cost of mailing a package, we start by obtaining the package weight and then apply various costs and surcharges depending on the weight: base cost of $10.00 for the first two pounds, $3.75 for each pound over two pounds, and an excess weight surcharge of $10.00 for packages over 70 pounds. If the package weighs more than 100 pounds, it is not accepted. The total cost is computed as $base\_cost + additional\_cost + extra\_cost$.

Step-by-step solution

Identifying the weight of the package

We will start by asking the user to input the weight of the package. The weight should be recorded in a variable called "weight".

Calculating the cost for the first two pounds

The cost of sending the package for the first two pounds is given as $10.00. We will store this value in a variable called "base_cost".

Calculating the cost for additional weight over two pounds

If the weight of the package exceeds two pounds, the cost for each additional pound (or fraction thereof) is given as $3.75. We will compute this additional cost using the following formula: \[ additional\_cost = max(0, ceil(weight - 2) * 3.75) \] Where "ceil" is the function that rounds up the input value to the nearest integer.

Checking if there is an excess weight surcharge and adding it to the cost

If the weight of the package is more than 70 pounds, an excess weight surcharge of $10.00 must be added to the cost. We will store this surcharge in a variable called "extra_cost" and add it to our calculations when necessary, i.e., if the weight is more than 70 pounds.

Checking if the package is overweight and providing appropriate response

If the weight of the package exceeds 100 pounds, the package is overweight and will not be accepted. In this case, we need to display an error message, and the program should not proceed with further calculations.

Calculating the total cost

We compute the total cost as follows: \[ total\_cost = base\_cost + additional\_cost + extra\_cost \]

Displaying the total cost

Finally, we display the total cost after all the calculations and deductions have been applied. If the package was overweight, the error message should have been displayed, and this step should not be reached.

Key concepts

Conditional Statements

Conditional statements are the backbone of decision-making within a program. They allow a program to execute different actions based on specific conditions, akin to asking the question, “What should I do if...?” For instance, in our package cost calculation exercise, conditional statements help determine:

• If a package weighs over two pounds, triggering an extra charge calculation.
• Whether to add a surcharge for packages exceeding 70 pounds.
• The necessity to halt the process if a package exceeds 100 pounds, displaying an error instead of continuing.

Let's think of an if-statement, a common type of conditional statement. You might write: ```python if weight > 70: extra_cost = 10.00 ``` This code checks whether the package is over 70 pounds, and if so, applies a surcharge. These imperative statements allow our program to be flexible, handling various possible inputs to provide the correct output.

Variables and Data Types

In programming, variables play an essential role in storing and manipulating data. A variable can be considered a storage location with a particular name, holding data of a specific type.
For instance, during the package cost calculation, you would create a variable called `weight` to store the user's input regarding the package weight. Depending on what type of information we are storing, variables can have different data types.

• Integers: These are whole numbers, positive or negative, and zero.
• Floats: These are decimal numbers, used when more precision is needed, such as monetary values.
• Strings: These are text, like an error message or a user’s name.

In our exercise, `base_cost`, `additional_cost`, and `total_cost` are floats because they represent monetary amounts. Using the right data types ensures our calculations remain accurate, particularly when dealing with money, where precision is crucial.

User Input Handling

Interacting with users often involves handling input, fulfilling the basic function of converting users' physical input into a digital format the software understands. It's vital for applications that need data from users to function properly.
In our mailing cost example, the program prompts users to enter the package's weight. We use the function to get this input and subsequently convert it to a numeric form suitable for calculations, usually a float for weights involving fractions using a line like: ```python weight = float(input('Enter package weight: ')) ``` Ensuring input is correctly handled and stored is crucial—if not, the program could behave unexpectedly or produce errors. Here, user input is directly linked to decisions and outputs later in the program, highlighting the importance of handling it accurately.