import Foundation
func checkString(string: String) -> Bool {
let digits = CharacterSet.decimalDigits
let stringSet = CharacterSet(charactersIn: string)
return digits.isSuperset(of: stringSet)
}
if checkString(string: "89301") {
print("The string contains only digits")
} else {
print("The string does not contain only digits")
}
/*
run:
The string contains only digits
*/