Assignment Overview

In this practice assignment, students will build a simple calculator that accepts two numbers and an arithmetic operation from the user, performs the selected calculation, and displays the result clearly.

This assignment is designed to help students combine several beginner programming concepts in one practical mini project. Students will practice reading user data, validating input, using arithmetic operators, applying conditions, handling invalid choices, avoiding division by zero, and formatting output properly.

Learning Objectives

After completing this assignment, students should be able to:

Prerequisites

Before attempting this assignment, students should revise the following topics:

Assignment Instructions

Build a simple calculator using language-neutral pseudocode. The calculator should ask the user for two numbers and one operation. Based on the selected operation, the program should calculate and display the result.

Calculator Requirements

Your calculator program must satisfy the following requirements.

Input → Process → Output Plan

Before writing pseudocode, students should understand the calculator using the IPO model.

Expected User Inputs

The calculator should read the following values from the user:

Example Input

First number: 20
Second number: 5
Operation: /

Expected Output

Result: 20 / 5 = 4

Operation Menu

Students may use either operation symbols or menu numbers. Both approaches are acceptable.

Option A: Symbol-Based Menu

Choose operation:
+ for Addition
- for Subtraction
* for Multiplication
/ for Division

Option B: Number-Based Menu

Choose operation:
1. Addition
2. Subtraction
3. Multiplication
4. Division

Validation Rules

The calculator should apply basic input validation.

Task 1: Write the Algorithm

Write an algorithm for building a simple calculator.

Expected Algorithm Structure

Step 1: Start
Step 2: Ask the user to enter the first number
Step 3: Read the first number
Step 4: Ask the user to enter the second number
Step 5: Read the second number
Step 6: Display operation menu
Step 7: Read operation choice
Step 8: If operation is addition, calculate sum
Step 9: If operation is subtraction, calculate difference
Step 10: If operation is multiplication, calculate product
Step 11: If operation is division, check second number is not zero
Step 12: If valid, calculate quotient
Step 13: Display result
Step 14: Stop

Task 2: Write Language-Neutral Pseudocode

Write pseudocode for the calculator using clear and readable steps.

Your Pseudocode Area

WRITE YOUR SIMPLE CALCULATOR PSEUDOCODE HERE

Task 3: Create a Trace Table

Use the following test case and complete the trace table.

Test Case

First Number = 12
Second Number = 4
Operation = *

Task 4: Test Your Calculator

Test your calculator using the following test cases.

Sample Solution: Algorithm

Step 1: Start
Step 2: Declare firstNumber, secondNumber, operation, and result
Step 3: Ask the user to enter the first number
Step 4: Read firstNumber
Step 5: Ask the user to enter the second number
Step 6: Read secondNumber
Step 7: Display operation choices
Step 8: Read operation
Step 9: If operation is "+", add firstNumber and secondNumber
Step 10: Else if operation is "-", subtract secondNumber from firstNumber
Step 11: Else if operation is "*", multiply firstNumber and secondNumber
Step 12: Else if operation is "/", check whether secondNumber is 0
Step 13: If secondNumber is 0, display division by zero error
Step 14: Otherwise divide firstNumber by secondNumber
Step 15: If operation is invalid, display invalid operation message
Step 16: Display result if calculation is successful
Step 17: Stop

Sample Solution: Basic Calculator Pseudocode

/*
Practice Assignment: Build a Simple Calculator
This program accepts two numbers and an operation,
then displays the calculated result.
*/

ENTRY POINT
    DECLARE firstNumber AS DECIMAL = 0.0
    DECLARE secondNumber AS DECIMAL = 0.0
    DECLARE operation AS TEXT = ""
    DECLARE result AS DECIMAL = 0.0
    DECLARE isCalculationSuccessful AS BOOLEAN = true

    DISPLAY "----- Simple Calculator -----"

    DISPLAY "Enter first number:"
    INPUT firstNumber

    DISPLAY "Enter second number:"
    INPUT secondNumber

    DISPLAY "Choose operation:"
    DISPLAY "+ for Addition"
    DISPLAY "- for Subtraction"
    DISPLAY "* for Multiplication"
    DISPLAY "/ for Division"

    INPUT operation

    IF operation == "+" THEN
        SET result = firstNumber + secondNumber

    ELSE IF operation == "-" THEN
        SET result = firstNumber - secondNumber

    ELSE IF operation == "*" THEN
        SET result = firstNumber * secondNumber

    ELSE IF operation == "/" THEN
        IF secondNumber == 0 THEN
            DISPLAY "Error: Division by zero is not allowed"
            SET isCalculationSuccessful = false
        ELSE
            SET result = firstNumber / secondNumber
        END IF

    ELSE
        DISPLAY "Error: Invalid operation selected"
        SET isCalculationSuccessful = false
    END IF

    IF isCalculationSuccessful == true THEN
        DISPLAY "----- Result -----"
        DISPLAY "First Number  : " + firstNumber
        DISPLAY "Second Number : " + secondNumber
        DISPLAY "Operation     : " + operation
        DISPLAY "Result        : " + result
    END IF
END ENTRY POINT

Sample Solution with Basic Input Validation

The following version includes simple validation ideas. It checks whether numeric input can be converted and whether the operation is valid.

/*
Calculator with basic input validation.
*/

ENTRY POINT
    DECLARE firstNumberText AS TEXT = ""
    DECLARE secondNumberText AS TEXT = ""
    DECLARE operation AS TEXT = ""
    DECLARE firstNumber AS DECIMAL = 0.0
    DECLARE secondNumber AS DECIMAL = 0.0
    DECLARE result AS DECIMAL = 0.0
    DECLARE isValid AS BOOLEAN = true

    DISPLAY "----- Simple Calculator -----"

    DISPLAY "Enter first number:"
    INPUT firstNumberText

    DISPLAY "Enter second number:"
    INPUT secondNumberText

    IF firstNumberText CANNOT BE CONVERTED TO DECIMAL THEN
        DISPLAY "Error: First number must be numeric"
        SET isValid = false
    ELSE IF secondNumberText CANNOT BE CONVERTED TO DECIMAL THEN
        DISPLAY "Error: Second number must be numeric"
        SET isValid = false
    ELSE
        SET firstNumber = CONVERT firstNumberText TO DECIMAL
        SET secondNumber = CONVERT secondNumberText TO DECIMAL
    END IF

    IF isValid == true THEN
        DISPLAY "Choose operation:"
        DISPLAY "+ Addition"
        DISPLAY "- Subtraction"
        DISPLAY "* Multiplication"
        DISPLAY "/ Division"

        INPUT operation

        IF operation == "+" THEN
            SET result = firstNumber + secondNumber

        ELSE IF operation == "-" THEN
            SET result = firstNumber - secondNumber

        ELSE IF operation == "*" THEN
            SET result = firstNumber * secondNumber

        ELSE IF operation == "/" THEN
            IF secondNumber == 0 THEN
                DISPLAY "Error: Division by zero is not allowed"
                SET isValid = false
            ELSE
                SET result = firstNumber / secondNumber
            END IF

        ELSE
            DISPLAY "Error: Invalid operation selected"
            SET isValid = false
        END IF
    END IF

    IF isValid == true THEN
        DISPLAY "----- Calculation Summary -----"
        DISPLAY "First Number  : " + firstNumber
        DISPLAY "Second Number : " + secondNumber
        DISPLAY "Operation     : " + operation
        DISPLAY "Result        : " + FORMAT_DECIMAL(result, 2)
    END IF
END ENTRY POINT

Bonus Task: Repeat Calculator Until User Exits

As a bonus challenge, modify the calculator so the user can perform multiple calculations without restarting the program.

Bonus Requirements

Bonus Pseudocode Idea

SET continueChoice = "yes"

WHILE continueChoice == "yes" DO
    PERFORM calculator steps

    DISPLAY "Do you want to calculate again? yes/no"
    INPUT continueChoice
END WHILE

DISPLAY "Thank you for using the calculator"

Bonus Task: Add More Operations

Students who finish early can extend the calculator by adding more operations.

Common Mistakes to Avoid

Submission Checklist

Before submitting, students should verify the following:

Evaluation Rubric

The assignment can be evaluated using the following rubric.

Sample Answer: Trace Table

For the test case 12, 4, and *, the trace table should look like this:

Mini Viva Questions

Quick Summary