Selection Sort Swift - Big Number Array

//Input array
var arr = ["31415926535897932384626433832795", "4", "66", "100"];
 
func comp(s1 : String, s2:String) -> Bool {
    
    let length1 = s1.characters.count
    let length2 = s2.characters.count
    
    if length1 < length2 {
        return true;
    }
    
    if length1 > length2 {
        return false;
    }
    
 
    if Int64(s1)! <  Int64(s2)! {
        return true;
    }
    
    
    if Int64(s1)! >  Int64(s2)! {
        return false;
    }
    
    return false;
    
}


//selection-sort 

var sortedArr = [String]()
var minIndex = 0;

for i in 0..<(arr.count - 1) {
    
    minIndex = i;
    
    for j in (i+1)..<arr.count {
  
           if comp(s1: arr[j], s2: arr[minIndex]) {
            
            minIndex = j;
   
        }
        
    }
    
    //swap old min value  with new min
    var temp = arr[i];
    arr[i] =  arr[minIndex];
    arr[minIndex] = temp;
       
}

   //Log the result.
   print(arr);