11.4. Using Multiple if statements

You can use more than one if statement in your code. Here’s an example of a calculation that uses two if statements. Let’s compute the total cost of an item where the price is based on the weight of the item. If the item weighs less than 1 pound then the price is 1.45 a pound. If the item weighs 1 pound or more the price is 1.15 a pound.

The program below is an attempt to do that. But it is broken in a subtle way. For one value of weight, the price will not be set to any value, so the calculation of total will fail with an error that something is not defined. Edit the code and change the first line so that weight has a different value. Run it again and see what changes. Try it in the codelens as well to see how the different values for weight changes the lines of code that are executed. Can you figure out the value of weight that will result in an error?

weight = 0.5 if weight < 1: price = 1.45 if weight > 1: price = 1.15 total = weight * price print(weight) print(price) print(total)

So how can we fix the bug? One way would be to change the second if to use >= so that there the program handles every situation correctly.

Another way we could solve the problem would be to set a price as a default, to assume that the weight if 1 or more. Then, we use an if to change change it only if the weight turns out to be less than 1.

weight = 0.5 price = 1.45 if weight >= 1: price = 1.15 total = weight * price print(weight) print(price) print(total)

Modify the top program to use >= in its second if. Then try both programs for weights of less than 1, 1, and more than 1. Are there values for weight that make the two programs above print different results when the same weight is used in both programs?

• No, they're always the same.
• The end result is the same.
• Yes, they're different if the weight is exactly 1 pound.
• If the weight is exactly 1 pound the price will be 1.15 in both programs.
• Yes, they're different if the weight is under 1 pound.
• If the weight is under 1 pound the price will be 1.45 in both programs.
• Yes, they're different if the weight is over 1 pound.
• If the weight is over 1 pound the price will be 1.15 in both programs.

Check your understanding

The following program should calculate the total price, but the lines are mixed up. The price is based on the weight. Items that weigh less than 2 pounds should cost 1.5. Items that weigh more than 2 pounds should cost 1.3. Drag the blocks from the left and place them in the correct order on the right. Be sure to also indent correctly!

        weight = 0.5
numItems = 5
if weight < 2:
---
    price = 1.50
---
if weight >= 2:
---
    price = 1.30
---
total = weight * price
---
print(weight)
print(price)
print(total)
        

Which of the following is true about the code below?

if (x > 2):
    x = x * 2
if (x > 4):
    x = 0
print(x)

• x will always equal 0 after this code executes for any value of x
• If x was set to 1 originally, then it would still equal 1.
• if x is greater than 2, the value in x will be doubled after this code executes
• What happens in the original when x is greater than 2?
• if x is greater than 2, x will equal 0 after this code executes
• If x is greater than 2, it will be set to 0.

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