Project Simple Calculator

Context

Build a command‑line calculator that reads two numbers and an operator (+, -, *, /), then prints the result.

This project combines:

• Reading user input (bufio, fmt.Scanln)
• Type conversion (strconv.ParseFloat)
• Conditional logic (switch)
• Error handling

Step‑by‑step code

package main

import (
    "bufio"
    "fmt"
    "os"
    "strconv"
    "strings"
)

func main() {
    reader := bufio.NewReader(os.Stdin)

    // Read first number
    fmt.Print("Enter first number: ")
    num1Str, _ := reader.ReadString('\n')
    num1, err1 := strconv.ParseFloat(strings.TrimSpace(num1Str), 64)
    if err1 != nil {
        fmt.Println("Invalid number")
        return
    }

    // Read operator
    fmt.Print("Enter operator (+, -, *, /): ")
    op, _ := reader.ReadString('\n')
    op = strings.TrimSpace(op)

    // Read second number
    fmt.Print("Enter second number: ")
    num2Str, _ := reader.ReadString('\n')
    num2, err2 := strconv.ParseFloat(strings.TrimSpace(num2Str), 64)
    if err2 != nil {
        fmt.Println("Invalid number")
        return
    }

    // Perform calculation
    var result float64
    switch op {
    case "+":
        result = num1 + num2
    case "-":
        result = num1 - num2
    case "*":
        result = num1 * num2
    case "/":
        if num2 == 0 {
            fmt.Println("Error: division by zero")
            return
        }
        result = num1 / num2
    default:
        fmt.Println("Invalid operator")
        return
    }

    fmt.Printf("%g %s %g = %g\n", num1, op, num2, result)
}

Example interaction

Enter first number: 10
Enter operator (+, -, *, /): /
Enter second number: 3
10 / 3 = 3.3333333333333335

Another example (division by zero)

Enter first number: 5
Enter operator (+, -, *, /): /
Enter second number: 0
Error: division by zero

Useful links

• strconv package
• bufio package
• fmt package