Checking if array value is valid number in Swift 4 - objective-c

Question

I have following code which is working in Objective-C:
NSScanner *scanner ;
for(int i = 0; i < [expression count]; i = i + 2)
{
scanner = [NSScanner scannerWithString:[expression objectAtIndex:i]];
BOOL isNumeric = [scanner scanInteger:NULL] && [scanner isAtEnd];
if(!isNumeric)
return false;
}
return true;
I need equivalent code in Swift 4. I have tried different things but couldn't work it out. The requirement is to check whether the elements of array are number or not.

Answer 1

To check if an object is a number (Int in your case), you could do two things:
Type check via is or as?
This only checks the type and not the content
let isNumberType = "1" is Int
print(isNumberType) //false because "1" is of type String
Creating an Int via it's initializer
This returns an Int? because it can fail so further check != nil
let something = "1"
let isNumber = Int(something) != nil
print(isNumber) //true because "1" can be made into an Int
NOTE: As per your example, you're checking only even elements, hence we will use stride(from:to:by:)
Solution #1:
Assuming you have an array of Strings, we can use the Int initializer to check if the string element can be a number, like so:
func check(expression: [String]) -> Bool {
for idx in stride(from: 0, to: expression.count, by: 2) {
let isNumeric = Int(expression[idx]) != nil
if isNumeric == false {
return false
}
}
return true
}
check(expression: ["1", "A", "2", "B", "3", "C"]) //true
check(expression: ["1", "A", "2", "B", "E", "C"]) //false
Solution #2:
Assuming your array is of type [Any] and you want to type check the alternate elements to be Int then use is, like so:
func check(expression: [Any]) -> Bool {
for idx in stride(from: 0, to: expression.count, by: 2) {
let isNumeric = expression[idx] is Int
if isNumeric == false {
return false
}
}
return true
}
check(expression: [1, "A", 2, "B", 3, "C"]) //true
check(expression: [1, "A", 2, "B", "3", "C"]) //false
The thing with [Any] is that it's elements can't be fed directly to the Int's initializer without bringing it into an acceptable type.
So in this example, for simplicity sake, we are just checking if the object is exactly of type Int or not.
Therefore, I doubt this one suits your requirement.

Answer 2

Try this:
var str = "1234456";
let scanner = Scanner(string: str);
let isNumeric = scanner.scanInt(nil) && scanner.isAtEnd
if !isNumeric {
print("not numeric")
} else {
print("is numeric")
}
Overall if you just want to check the given string is an parsable Integer, I recommend you try :
var expressions = ["1234456","abcd"];
for str in expressions {
if let isNumeric = Int(str) {
print("is numeric")
} else {
print("not numeric")
}
}