A calculator project in Scratch is a fun way to combine math, coding, and design. Students build number and operation buttons, then make the program remember what the user clicks. The project matters because it shows how computers follow clear step-by-step instructions.
It also helps students practice debugging, variables, and user interface design.
Key Facts
- Use variables to store values: firstNumber, secondNumber, operation, and display.
- When a digit button is clicked, update the display by joining the old display and the new digit.
- For addition, calculate result = firstNumber + secondNumber.
- For subtraction, calculate result = firstNumber - secondNumber.
- For multiplication, calculate result = firstNumber × secondNumber.
- For division, calculate result = firstNumber ÷ secondNumber, but check that secondNumber is not 0.
Vocabulary
- Sprite
- A sprite is an object in Scratch, such as a calculator button, that can have code, costumes, and sounds.
- Variable
- A variable is a named storage space that holds information, such as a number or the selected operation.
- Operator
- An operator is a symbol or block that performs a math action, such as +, -, ×, or ÷.
- Event
- An event is something that starts code running, such as clicking a button sprite.
- Debugging
- Debugging is the process of finding and fixing mistakes in a program.
Common Mistakes to Avoid
- Forgetting to reset the display after pressing an operation button. This is wrong because the next number may get joined onto the first number instead of starting a new input.
- Saving numbers as text but trying to calculate without converting them. This can cause Scratch to join values like words instead of treating them as numbers.
- Using the same code for every button without changing the digit value. This is wrong because each button must add its own number, such as 3 for the 3 button.
- Allowing division by zero. This is wrong because a number cannot be divided by 0, so the calculator should show an error message instead.
Practice Questions
- 1 A user clicks 1, 2, +, 8, =. What should the display show, and what values should firstNumber and secondNumber store before the final calculation?
- 2 A calculator stores firstNumber = 36, operation = ÷, and secondNumber = 4. What result should appear on the display?
- 3 Explain why a calculator program needs separate variables for the first number, the second number, and the operation instead of using only one variable for everything.