Swift – Implementing a basic calculator

In this tutorial, we will learn how to implement a basic calculator in Swift that performs addition, subtraction, multiplication, and division. We will handle user inputs and display the results for each operation.

Understanding the Problem

A basic calculator performs operations such as addition, subtraction, multiplication, and division on two numbers. In this implementation, we will:

  • Take two numbers as inputs.
  • Allow the user to choose an operation.
  • Perform the selected operation and display the result.
  • Handle edge cases, such as division by zero.

Swift Program for a Basic Calculator

Here’s the implementation:

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import Foundation

// Function to perform calculator operations
func calculate(_ num1: Double, _ num2: Double, operation: String) -> Double? {
    switch operation {
    case "+":
        return num1 + num2
    case "-":
        return num1 - num2
    case "*":
        return num1 * num2
    case "/":
        if num2 != 0 {
            return num1 / num2
        } else {
            print("Error: Division by zero is not allowed.")
            return nil
        }
    default:
        print("Invalid operation. Please choose +, -, *, or /.")
        return nil
    }
}

// Example usage
let num1 = 10.0
let num2 = 5.0

if let result = calculate(num1, num2, operation: "+") {
    print("\(num1) + \(num2) = \(result)")
}

if let result = calculate(num1, num2, operation: "-") {
    print("\(num1) - \(num2) = \(result)")
}

if let result = calculate(num1, num2, operation: "*") {
    print("\(num1) * \(num2) = \(result)")
}

if let result = calculate(num1, num2, operation: "/") {
    print("\(num1) / \(num2) = \(result)")
}

Explanation:

  • calculate(_:_:operation:): A function that takes two numbers and an operation (+, -, *, /) as inputs and performs the corresponding calculation.
  • switch operation: Determines which operation to perform based on the input operator.
  • Handles division by zero by checking if num2 is zero before performing the division.
  • Returns nil for invalid operations or division by zero.

Handling User Input

To make the program interactive, you can use readLine() to take inputs from the user:

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print("Enter the first number:")
if let input1 = readLine(), let num1 = Double(input1) {
    print("Enter the second number:")
    if let input2 = readLine(), let num2 = Double(input2) {
        print("Choose an operation (+, -, *, /):")
        if let operation = readLine() {
            if let result = calculate(num1, num2, operation: operation) {
                print("Result: \(result)")
            }
        } else {
            print("Invalid operation.")
        }
    } else {
        print("Invalid input for the second number.")
    }
} else {
    print("Invalid input for the first number.")
}

Complete Swift Program

Here’s the complete program, combining static examples and interactive user inputs:

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import Foundation

// Function to perform calculator operations
func calculate(_ num1: Double, _ num2: Double, operation: String) -> Double? {
    switch operation {
    case "+":
        return num1 + num2
    case "-":
        return num1 - num2
    case "*":
        return num1 * num2
    case "/":
        if num2 != 0 {
            return num1 / num2
        } else {
            print("Error: Division by zero is not allowed.")
            return nil
        }
    default:
        print("Invalid operation. Please choose +, -, *, or /.")
        return nil
    }
}

// Interactive Calculator
print("Enter the first number:")
if let input1 = readLine(), let num1 = Double(input1) {
    print("Enter the second number:")
    if let input2 = readLine(), let num2 = Double(input2) {
        print("Choose an operation (+, -, *, /):")
        if let operation = readLine() {
            if let result = calculate(num1, num2, operation: operation) {
                print("Result: \(result)")
            }
        } else {
            print("Invalid operation.")
        }
    } else {
        print("Invalid input for the second number.")
    }
} else {
    print("Invalid input for the first number.")
}

// Static Examples
let example1 = calculate(12, 4, operation: "+") // Addition
print("12 + 4 = \(example1 ?? 0)")

let example2 = calculate(12, 4, operation: "/") // Division
print("12 / 4 = \(example2 ?? 0)")

let example3 = calculate(12, 0, operation: "/") // Division by zero
print("12 / 0 = \(example3 ?? 0)")

Output:

Enter the first number:
10
Enter the second number:
20
Choose an operation (+, -, *, /):
+
Result: 30.0
12 + 4 = 16.0
12 / 4 = 3.0
Error: Division by zero is not allowed.
12 / 0 = 0.0
Program ended with exit code: 0

This program can handle user inputs dynamically while also providing static examples to test different operations. It includes error handling for invalid inputs and division by zero.

Swift - Implement a Basic Calculator (add, subtract, multiply, divide)