how to use "0" to fill the rest space of the first string when I copy scond string into the first string in swift?

Question

For example, I have a string: let one = "1" , and I have another string:

let two = "123"

Now I have a function:

func myfunc(head:String,body:String) -> String
{
   //following are pseudo code
   var return_string: String
   return_string[0...2] = head
  // the passing parameter: head's length will be equal or less than 3 charactors
   //if the string: head's length is less than 3, the other characters will be filled via "0"
     return_string[3...end] = body//the rest of return_string will be the second passing parameter: body


}

For example, if I call this function like this:

myfunc(one,"hello")

it will return 001hello, if I call it like this:

myfunc(two,"hello")

it will return 123hello if I call it like this:

myfunc("56","wolrd")

it will return

056world

Here is my extension to String:

extension String {
var length: Int {
    return self.characters.count
}
subscript (i:Int) -> Character{
    return self[self.startIndex.advancedBy(i)]
}
subscript (i: Int) -> String {
    return String(self[i] as Character)
}

subscript (r: Range<Int>) -> String {
    return substringWithRange(Range(start: startIndex.advancedBy(r.startIndex), end: startIndex.advancedBy(r.endIndex)))
}
}

what should I do ? How to insert 0 at the beginning of the string:return_value?

I don't know how to insert 0 into the head of the string:return_value — beasone, Nov 17 '15 at 19:59
[some info on concatenating strings](http://stackoverflow.com/questions/24034174/how-do-i-concatenate-strings-in-swift) — R Menke, Nov 17 '15 at 20:03

score 3 · Accepted Answer · answered Nov 17 '15 at 20:07

There are many possible approaches, this is just one:

func myfunc(head:String, _ body:String) -> String
{
    return String(("000" + head).characters.suffix(3)) + body
}

It works by taking the last three characters of "000" + head:

myfunc("1", "hello")   // "001hello"
myfunc("123", "hello") // "123hello"
myfunc("56", "world")  // "056world"

score 0 · Answer 2 · answered Nov 17 '15 at 20:05

First off, you don't need the String extension. This method will append 0's to the beginning of head until it is 3 characters, then concatenate the two strings.

func myFunc(var head: String, body: String) -> String {
    while head.characters.count < 3 {
        head.insert("0", atIndex: head.startIndex)
    }
    head = head.substringToIndex(head.startIndex.advancedBy(3))
    return head + body
}

how to use "0" to fill the rest space of the first string when I copy scond string into the first string in swift?

2 Answers2