In Kotlin, we can use the toDoubleOrNull() function to check if a string is a number or not. This function returns a Double if the string is a valid number or null if it is not. Here's an example:
fun main() {
val str1 = "123"
val str2 = "12.3"
val str3 = "abc"
val num1 = str1.toDoubleOrNull()
val num2 = str2.toDoubleOrNull()
val num3 = str3.toDoubleOrNull()
if (num1 != null) {
println("$str1 is a number")
} else {
println("$str1 is not a number")
}
if (num2 != null) {
println("$str2 is a number")
} else {
println("$str2 is not a number")
}
if (num3 != null) {
println("$str3 is a number")
} else {
println("$str3 is not a number")
}
}
Output:
123 is a number
12.3 is a number
abc is not a number
In this example, we have three strings str1, str2, and str3. str1 and str2 are valid numbers while str3 is not. We use the toDoubleOrNull() function to convert each string to a Double. If the conversion is successful and the resulting Double is not null, we print that the string is a number. Otherwise, we print that the string is not a number.