Lab Activity: Building Calculator

Objectives

• Practice using conditional statements (if/elif/else).

• Use a while loop to keep repeating tasks until exit.

• Apply break and continue for loop control.

• Build a simple menu-driven calculator program.

• Handle errors such as invalid input and division by zero.

step-by-step instructions

Step 1: Plan the Menu

Menu Options:

1. Add two numbers

2. Subtract two numbers

3. Multiply two numbers

4. Divide two numbers

5. Exit the program

Step 2: Code the Loop and Menu

We’ll use while True: so the menu repeats until the user selects “Exit”.

def run_calculator():
    while True:
        # Display menu
        print("Select an operation:")
        print("1. Add")
        print("2. Subtract")
        print("3. Multiply")
        print("4. Divide")
        print("5. Exit")

        choice = input("Enter choice (1/2/3/4/5): ")

        if choice == '5':
            print("Exiting the calculator.")
            break

Step 3: Handle User Input

Add input for numbers and perform operations:

        elif choice in ('1', '2', '3', '4'):
            try:
                a = float(input("Enter first number: "))
                b = float(input("Enter second number: "))
            except ValueError:
                print("Invalid input! Please enter numbers only.")
                continue

            if choice == '1':
                print("Result:", a + b)
            elif choice == '2':
                print("Result:", a - b)
            elif choice == '3':
                print("Result:", a * b)
            elif choice == '4':
                if b == 0:
                    print("Error: Division by zero is not allowed.")
                else:
                    print("Result:", a / b)

Step 4: Handle Invalid Choices

If the user enters something not in the menu:

        else:
            print("Invalid choice. Please enter a number between 1 and 5.")

Complete Program

def run_calculator():
    while True:
        # Display menu
        print("nSelect an operation:")
        print("1. Add")
        print("2. Subtract")
        print("3. Multiply")
        print("4. Divide")
        print("5. Exit")

        choice = input("Enter choice (1/2/3/4/5): ")

        if choice == '5':
            print("Exiting the program. Goodbye!")
            break
        elif choice in ('1', '2', '3', '4'):
            try:
                a = float(input("Enter first number: "))
                b = float(input("Enter second number: "))
            except ValueError:
                print("Invalid input! Please enter numbers only.")
                continue

            if choice == '1':
                print("Result:", a + b)
            elif choice == '2':
                print("Result:", a - b)
            elif choice == '3':
                print("Result:", a * b)
            elif choice == '4':
                if b == 0:
                    print("Error: Division by zero is not allowed.")
                else:
                    print("Result:", a / b)
        else:
            print("Invalid choice. Please enter a number between 1 and 5.")


run_calculator()

Sample Interaction

Select an operation:
1. Add
2. Subtract
3. Multiply
4. Divide
5. Exit
Enter choice (1/2/3/4/5): 1
Enter first number: 10
Enter second number: 25
Result: 35.0

Enter choice (1/2/3/4/5): 4
Enter first number: 10
Enter second number: 0
Error: Division by zero is not allowed.

Enter choice (1/2/3/4/5): 9
Invalid choice. Please enter a number between 1 and 5.

Enter choice (1/2/3/4/5): 5
Exiting the program. Goodbye!

Key Concepts Learned

• Using while True for looping until exit.

• Handling decisions with if/elif/else.

• Using break and continue effectively.

• Building a user-friendly, interactive program.