Correctly parse negative numbers and calculate temperatures.

src/main/kotlin/Main.kt

@@ -7,12 +7,18 @@ fun Double.round(): String{
     return String.format("%.2f", this)
 }
 
+fun cleanNumberString(input: String): String{
+    return input
+        .replace(",",".")
+        .replace(" ", "")
+}
+
 fun extractNumbers(pattern: String, text: String?): List<Double> {
     val matches = Regex(pattern).findAll(text ?: "")
     return matches
         .map { it.groups[1]?.value?.lowercase() }
         .filter { it != null }
-        .map { it!!.replace(",", ".").toDouble() }
+        .map { cleanNumberString(it!!).toDouble() }
         .toList()
 }
 
@@ -47,16 +53,16 @@ fun convertKmh(event: MessageCreateEvent) {
 }
 
 fun convertF(event: MessageCreateEvent){
-    for (fahrenheit in extractNumbers("(\\d+[,.]*\\d*)\\s*f", event.message.content)) {
-        val celsius = (5/9) * (fahrenheit - 32)
+    for (fahrenheit in extractNumbers("(-*\\d+[,.]*\\d*)\\s*f", event.message.content)) {
+        val celsius = (5.0/9.0) * (fahrenheit - 32)
         val kelvin = celsius + 273.15
         event.channel.sendMessage("${fahrenheit.round()} °F = ${celsius.round()} °C = ${kelvin.round()} K")
     }
 }
 
 fun convertC(event: MessageCreateEvent){
-    for (celsius in extractNumbers("(\\d+[,.]*\\d*)\\s*c", event.message.content)) {
-        val fahrenheit = ((9/5) * celsius) + 32
+    for (celsius in extractNumbers("(-*\\d+[,.]*\\d*)\\s*c", event.message.content)) {
+        val fahrenheit = ((9.0/5.0) * celsius) + 32
         val kelvin = celsius + 273.15
         event.channel.sendMessage("${celsius.round()} °C = ${fahrenheit.round()} °F = ${kelvin.round()} K")
     }