--- title: "A menu that keeps showing" subtitle: "Console bridge: text in, text out · Menus and testing · Lesson 9" --- # A menu that keeps showing **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Ticket machines, ATMs and the settings on a phone are all menus: show the choices, wait for one, do it, and show the menu again. :::teacher-note **In one sentence:** Students build a menu with while True, choose with if and elif, and leave with break. **Students should be able to say:** I can use while True with break to make a menu that keeps showing. I can add a choice to a menu with elif. I can build my own small menu app. **Width:** the unmarked parts are the floor every student does (predict, run, investigate and make). Typical adds the modify practice; wider adds the real-world contexts. They add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Predict `while True` and `break` are new. Read the program. What is shown? ```python total = 0 while True: choice = input("1 add $5, 2 pay: ") if choice == "1": total += 5 print("Total: $" + str(total)) elif choice == "2": print("Pay $" + str(total)) break else: print("Please choose 1 or 2.") print("Thank you") ``` :::keep-together **You type 1, 1, 3, then 2. What does the program show?** ☐ Total: $5, Total: $10, Please choose 1 or 2., Pay $10, Thank you ☐ Total: $5, Total: $10, Please choose 1 or 2., and then the program stops ☐ It never stops, even after 2 ☐ Total: $5, Total: $10, Please choose 1 or 2., Pay $10, and then it asks again My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** Total: $5, Total: $10, Please choose 1 or 2., Pay $10, Thank you. break leaves the whole loop at once, not just the if, so the program carries on after the loop and ends. ::: ## Run Run the program in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Investigate ```python total = 0 while True: choice = input("1 add $5, 2 pay: ") if choice == "1": total += 5 print("Total: $" + str(total)) elif choice == "2": print("Pay $" + str(total)) break else: print("Please choose 1 or 2.") print("Thank you") ``` :::keep-together ### Follow a session **You type 1, 1, 3, 2. Fill in the total after each choice and whether the loop goes round again.** {{rows 1}} | choice | total after | loop goes round again | |---|---|---| | 1 | 5 | yes | | 1 | | | | 3 | | | | 2 | | | ::: :::teacher-note **Answer:** 10, yes, 10, yes, 10, no A wrong choice (3) changes nothing, and the menu shows again. Only 2 runs break. ::: :::keep-together ### Spot the bug **Choosing 2 shows Pay $10, but then the menu comes back and the program never ends. Click the line where something is missing.** ``` 1 total = 0 2 while True: 3 choice = input("1 add $5, 2 pay: ") 4 if choice == "1": 5 total += 5 6 elif choice == "2": 7 print("Pay $" + str(total)) 8 else: 9 print("Please choose 1 or 2.") 10 print("Thank you") ``` Line: {{field-15}} Why is it wrong? {{lines-2}} ::: :::teacher-note **Answer:** line 7 Nothing ever runs break, so while True never ends. The pay branch needs a break line after the print. ::: :::keep-together ### What does break do? **What does break do when it runs inside an if inside a while True?** ☐ Stops the program ☐ Leaves only the if ☐ Skips to the next pass ☐ Leaves the whole loop at once ::: :::teacher-note **Answer:** Leaves the whole loop at once break ends the loop it is in. The program continues with the first line after the loop. ::: :::typical ## Modify Add a drink for $2 as choice 3. Paying becomes choice 4. Update the menu text too. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. ```python total = 0 while True: choice = input("1 add $5, 3 drink $2, 4 pay: ") if choice == "1": total += 5 print("Total: $" + str(total)) elif choice == "3": total += 2 print("Total: $" + str(total)) elif choice == "4": print("Pay $" + str(total)) break else: print("Please choose 1, 3 or 4.") print("Thank you") ``` ::: ::: ## Mix it up This mixes the last lessons: a loop that repeats, and an answer stored again each pass. ```python total = 0 while True: choice = input("1 add $5, 2 pay: ") if choice == "1": total += 5 print("Total: $" + str(total)) elif choice == "2": print("Pay $" + str(total)) break else: print("Please choose 1 or 2.") print("Thank you") ``` :::keep-together **You type 3, 3, 2. How many times does the menu question appear?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 3 Each pass asks once. 3 and 3 are wrong choices that go round again, and 2 asks a third time before it breaks. ::: ## Make Make your own menu app: a café, a game shop, a quiz scoreboard or a unit converter. It needs `while True`, at least three choices, a reply for a wrong choice, and a way to quit. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. ```python total = 0 while True: choice = input("1 coffee $4, 2 cake $5, 3 pay: ") if choice == "1": total += 4 print("Coffee added. Total: $" + str(total)) elif choice == "2": total += 5 print("Cake added. Total: $" + str(total)) elif choice == "3": break else: print("Please choose 1, 2 or 3.") print("Please pay $" + str(total)) ``` ::: ## Exit ticket :::keep-together **What does break do, and what happens to the program after it?** {{lines-3}} ::: :::teacher-note **Answer:** break leaves the loop at once. The program carries on with the first line after the loop. :::