Kotlin program to create a simple calculator

Kotlin program to create a simple calculator:

In this post, we will learn how to create a simple calculator program in Kotlin. We will write a program that will take two numbers as the inputs from the user and perform basic arithmetic operations i.e. sum, subtraction, multiplication, or division based on user input.

I will show you two ways to solve this problem: By using if-else if-else statements or by using when expression.

Method 1: Kotlin program of a simple calculator by using if-else if-else statements:

Let’s write down a program by using if-else if-else statements:

fun main() {
    println("Enter the numbers:")
    val firstNumber = readLine()?.toDoubleOrNull()
    val secondNumber = readLine()?.toDoubleOrNull()

    if (firstNumber != null && secondNumber != null) {
        println("Enter +, -, * or /:")
        val o = readLine().toString()[0]
        var result: Double? = null

        if (o == '+') {
            result = firstNumber + secondNumber
        } else if (o == '-') {
            result = firstNumber - secondNumber
        } else if (o == '*') {
            result = firstNumber * secondNumber
        } else if (o == '/') {
            result = firstNumber / secondNumber
        } else {
            println("Please enter a valid operator.")
        }

        if (result != null) {
            println("$firstNumber $o $secondNumber = $result")
        }
    } else {
        print("Please enter valid inputs")
    }
}

Here,

The program asks the user to enter the numbers.
It is using readLine() method to read the user entered value and converts it to a double. These values are stored in the firstNumber and secondNumber variables.
If the entered numbers are not null, it asks the user to enter the operator symbol. It reads the operator symbol and stores it in the variable o.
The if, else-if, else blocks checks the value of the variable o and based on its value, it calculates the result.
The last if block is used to print the final result.

If you run this program, it will print outputs as below:

Enter the numbers:
23
33
Enter +, -, * or /:
+
23.0 + 33.0 = 56.0

Enter the numbers:
33
56
Enter +, -, * or /:
*
33.0 * 56.0 = 1848.0

Enter the numbers:
133
4
Enter +, -, * or /:
-
133.0 - 4.0 = 129.0

Method 2: Kotlin program of a simple calculator by using when expression:

The when expression in Kotlin works similar to Java switch statement. We can also use it instead of if-else if-else conditions. Let’s modify the above program to use when expression instead of if-else if-else blocks:

fun main() {
    println("Enter the numbers:")
    val firstNumber = readLine()?.toDoubleOrNull()
    val secondNumber = readLine()?.toDoubleOrNull()

    if (firstNumber != null && secondNumber != null) {
        println("Enter +, -, * or /:")
        val o = readLine().toString()[0]
        var result: Double? = null

        when (o) {
            '+' -> {
                result = firstNumber + secondNumber
            }
            '-' -> {
                result = firstNumber - secondNumber
            }
            '*' -> {
                result = firstNumber * secondNumber
            }
            '/' -> {
                result = firstNumber / secondNumber
            }
            else -> {
                println("Please enter a valid operator.")
            }
        }

        if (result != null) {
            println("$firstNumber $o $secondNumber = $result")
        }
    } else {
        print("Please enter valid inputs")
    }
}

It will print similar results.

Enter the numbers:
123
23
Enter +, -, * or /:
+
123.0 + 23.0 = 146.0

Enter the numbers:
55
99
Enter +, -, * or /:
*
55.0 * 99.0 = 5445.0

CodeVsColor

Kotlin program to create a simple calculator