In Swift, you can use the Double() initializer to check if a string represents a number. Here's an example:
let string1 = "123"
let string2 = "3.14"
let string3 = "hello"
if let number1 = Double(string1) {
print("\(string1) is a number")
} else {
print("\(string1) is not a number")
}
if let number2 = Double(string2) {
print("\(string2) is a number")
} else {
print("\(string2) is not a number")
}
if let number3 = Double(string3) {
print("\(string3) is a number")
} else {
print("\(string3) is not a number")
}
Output:
123 is a number
3.14 is a number
hello is not a number
In the example above, we use the Double() initializer to try to convert the string into a double-precision floating-point number. If the conversion is successful, we print a message saying that it's a number. Otherwise, we print a message saying that it's not a number.