Verbatim Teaching Script: “if-elif Conditional Statements”
Students, just now the teacher noticed the class duty roster. From Monday to Friday, there are many diligent “little bees” on duty. I’d like to ask: which students are on duty on Monday? Please raise your hands. Yes, I see you. Now, students, do you remember who the students on duty on Monday are? That’s right, there are six students in total.
Now suppose we take three classes as a unit and give you a student’s name. Can you quickly tell which day of the week this student is on duty? Do you have any good ideas? You there—yes, you mentioned memorizing it with a rhyme or mnemonic. Are there any better methods? You—right, we can use a program to output the result. So, what kind of statement should we use to represent multiple conditions? Today, we are going to learn another conditional statement in Python: if-elif-else.
Next, please work in pairs with your desk mates. Analyze how to use if-elif-else to solve the problem of matching student names to duty days. You have 8 minutes. Begin.
Time’s up. While walking around, I saw everyone actively discussing. Which group would like to share your ideas? You, please. You said that we can input a student’s name and determine which day they are on duty by matching the name and outputting the corresponding weekday. Any additions? Group Five, please share. They suggested creating five arrays corresponding to Monday through Friday, placing each student’s name into the appropriate array, and then judging which day to output. That’s a very important point. Please sit down. Excellent work. It’s clear that everyone has previewed today’s lesson well.
Next, let’s integrate everyone’s ideas. Please think independently and draw a flowchart. You have 5 minutes. Begin.
Time’s up. This student, please come up and present your flowchart. You explained that first we input the student’s name. If Xiaohua is in Monday’s array, then output Monday, and so on. Now, please try to write a multi-branch conditional statement. Here’s a hint from the teacher: use elif for additional conditional clauses. Let’s ask this student to write their answer on the blackboard. Students, compare it with your own code. Which parts need modification? You said the final elif should be changed to else, to indicate that when none of the conditions are met, the statements under else are executed. You also mentioned paying attention to indentation and colons. Very careful observations. I hope everyone writes carefully when coding. Now please use the if-elif statements you’ve learned to implement the algorithm you designed. I see that everyone has written it correctly and avoided the earlier issues.
Now that we’ve written the statements, what is their execution process? Please discuss this in pairs. In a moment, we’ll ask one group to explain. You have 7 minutes. Begin.
I see students discussing quietly. Time’s up. Group Two, please explain the execution process. They used the flowchart to explain that the program checks each condition in order. If a condition is satisfied, it outputs the result; if none are satisfied, it outputs an error message. Their explanation combined diagrams and text and was very clear. Based on the flowchart on the screen, we can summarize the execution process of if-elif statements: the program starts from the if condition and checks conditions one by one. If a condition is true, the corresponding block of code is executed and the program exits the if structure. If the condition is false, it moves on to the next condition. If all conditions are false, the else block is executed.
Now that we’ve finished learning the new knowledge, please write a complete program that implements this process. Students who finish early may think about real-life situations that require checking multiple conditions and write corresponding programs. Let’s invite some students to present their work. Some students approached the problem from a mathematics perspective, writing a program to compare three numbers and find the maximum. Others took inspiration from daily life and wrote a taxi fare calculation program. All of your programs were well-structured and correctly formatted.
As today’s lesson comes to an end, what have you learned from this class? You said that you’ve learned the format and execution process of if-elif statements. It seems everyone has mastered today’s content. In fact, programming is very close to our daily life and studies, and it’s not as difficult as it may seem. The teacher hopes that you will continue to think actively and express your ideas in class just like today.
Finally, here is a homework assignment: please compare the characteristics of the three types of if statements and organize them into a table.
That’s all for today’s lesson. Goodbye, students.