Add solution for Challenge 18 (#1193)

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>

Author: goholic

challenge-18/submissions/goholic/solution-template.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	// Example usage
+	celsius := 25.0
+	fahrenheit := CelsiusToFahrenheit(celsius)
+	fmt.Printf("%.2f°C is equal to %.2f°F\n", celsius, fahrenheit)
+
+	fahrenheit = 68.0
+	celsius = FahrenheitToCelsius(fahrenheit)
+	fmt.Printf("%.2f°F is equal to %.2f°C\n", fahrenheit, celsius)
+}
+
+// CelsiusToFahrenheit converts a temperature from Celsius to Fahrenheit
+// Formula: F = C × 9/5 + 32
+func CelsiusToFahrenheit(celsius float64) float64 {
+	fahrenheit := (celsius * (9.0 / 5.0)) + 32
+	return Round(fahrenheit, 2)
+}
+
+func FahrenheitToCelsius(fahrenheit float64) float64 {
+	celsius := (fahrenheit - 32) * (5.0 / 9.0)
+	return Round(celsius, 2)
+}
+
+func Round(value float64, decimals int) float64 {
+	precision := math.Pow10(decimals)
+	return math.Round(value*precision) / precision
+}
+