Determine if a string starts with a number in Kotlin

This post will check if a string starts with a number or not in Kotlin.

A simple solution to check if the first character of the string is a digit is using the isDigit() function, which provides support for all Unicode digits.

fun main() {

val s = "7 Wonders of the World"

println(s.isNotEmpty() && s[0].isDigit()) // true

}

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Another solution is to extract the first character from the given string and check if that character falls under the numeric ASCII range or not.

fun main() {

val s = "7 Wonders of the World"

println(s.isNotEmpty() && s[0] >= '0' && s[0] <= '9') // true

}

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In Kotlin, two comparisons should be converted to a range check:

fun main() {

val s = "7 Wonders of the World"

println(s.isNotEmpty() && s[0] in '0'..'9') // true

}

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Here’s an alternate version using the any() function. It returns true if at least one element matches the supplied predicate.

fun main() {

val s = "7 Wonders of the World"

println(s.isNotEmpty() && ('0'..'9').any { it == s[0] }) // true

}

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Note that all the above solutions validate that the string is not empty to avoid string index out of range exception. That’s all about checking if a string starts with a number in Kotlin.

Determine if a string starts with a number in Kotlin

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