how can i do For Loop Properly - ios

Question

I want to add " 5 " in my arrays in every 3rd position
var myList: [String] = ["U.S", "Spain", "China", "Brazil", "India" , "Canada", "Germany", "UK", "Dubai", "Russia", "Japan", "Italy", "France", "Australia", "Thailand", "Mexico"]
var i = 0
for name in 0...myList.count {
i = i + 1
if i % 3 == 0 {
myList.insert("\(5)", at: i )
}
}
print("\(myList)")
OutPut is:
["U.S", "Spain", "China", "5", "Brazil", "India", "5", "Canada", "Germany", "5", "UK", "Dubai", "5", "Russia", "Japan", "5", "Italy", "France", "Australia", "Thailand", "Mexico"]
but after 16 position in array , I am not able to put all 5 in my arrays because of arrays that is myList have total 16 counts ....so how I can able to put 5 in my Arrays properly

Answer 1

The problem there is that you are mutating the array (changing its elements while iterating it), so what you actually need to do is to insert your elements in reverse order. Try like this:
var myList = ["U.S", "Spain", "China", "Brazil", "India", "Canada", "Germany", "UK", "Dubai", "Russia", "Japan", "Italy", "France", "Australia", "Thailand", "Mexico" ]
for index in myList.indices.dropFirst().reversed() where index % 3 == 0 {
myList.insert("5", at: index)
}
print(myList) // "["U.S", "Spain", "China", "5", "Brazil", "India", "Canada", "5", "Germany", "UK", "Dubai", "5", "Russia", "Japan", "Italy", "5", "France", "Australia", "Thailand", "5", "Mexico"]\n"