So, basically, I did the tutorial to create a random number on the website of Microsoft Azure and now I am trying to add some functionalities, including their suggestion add a minimum number.
The initial code to generate just one number, max, is:
operation SampleRandomNumberInRange(max : Int) : Int {
// mutable means variables that can change during computation
mutable output = 0;
// repeat loop to generate random numbers until it generates one that is less or equal to max
repeat {
mutable bits = new Result[0];
for idxBit in 1..BitSizeI(max) {
set bits += [GenerateRandomBit()];
}
// ResultArrayAsInt is from Microsoft.Quantum.Convert library, converts string to positive integer
set output = ResultArrayAsInt(bits);
} until (output <= max);
return output;
}
#EntryPoint()
operation SampleRandomNumber() : Int {
// let declares var which don't change during computation
let max = 50;
Message($"Sampling a random number between 0 and {max}: ");
return SampleRandomNumberInRange(max);
}
Everything works well. Now, I want to generate two numbers so I would like to create a function TwoSampleRandomNumbersInRange but I can't figure out how to make the function return a result such as "Int, Int", I tried a few things including the follow:
operation TwoSampleRandomNumbersInRange(min: Int, max : Int) : Int {
// mutable means variables that can change during computation
mutable output = 0;
// repeat loop to generate random numbers until it generates one that is less or equal to max
repeat {
mutable bits = new Result[0];
for idxBit in 1..BitSizeI(max) {
set bits += [GenerateRandomBit()];
}
for idxBit in 1..BitSizeI(min) {
set bits += [GenerateRandomBit()];
}
// ResultArrayAsInt is from Microsoft.Quantum.Convert library, converts string to positive integer
set output = ResultArrayAsInt(bits);
} until (output >= min and output <= max);
return output;
}
To generate two numbers, I tried this:
operation TwoSampleRandomNumbersInRange(min: Int, max : Int) : Int, Int {
//code here
}
...but the syntax for the output isn't right.
I also need the output:
set output = ResultArrayAsInt(bits);
to have two numbers but ResultArrayAsInt, as the name says, just returns an Int. I need to return two integers.
Any help appreciated, thanks!
The return of an operation has to be a data type, in this case to represent a pair of integers you need a tuple of integers: (Int, Int).
So the signature of your operation and the return statement will be
operation TwoSampleRandomNumbersInRange(min: Int, max : Int) : (Int, Int) {
// code here
return (integer1, integer2);
}
I found the answer to my own question, all I had to do was:
operation SampleRandomNumberInRange(min: Int, max : Int) : Int {
// mutable means variables that can change during computation
mutable output = 0;
// repeat loop to generate random numbers until it generates one that is less or equal to max
repeat {
mutable bits = new Result[0];
for idxBit in 1..BitSizeI(max) {
set bits += [GenerateRandomBit()];
}
// ResultArrayAsInt is from Microsoft.Quantum.Convert library, converts string to positive integer
set output = ResultArrayAsInt(bits);
} until (output >= min and output <= max);
return output;
}
#EntryPoint()
operation SampleRandomNumber() : Int {
// let declares var which don't change during computation
let max = 50;
let min = 10;
Message($"Sampling a random number between {min} and {max}: ");
return SampleRandomNumberInRange(min, max);
}
}
[Update] I spent a lot of time studying #Hovercouch's fantastic solution (see his solution below). I took his solution, along with Peter Krien's insights and wrote up a summary: 3 ways to model the set of non-negative even numbers. I welcome your comments.
I am trying to create an Alloy model that defines a set of integers. I want to constrain the set to the integers 0, 2, 4, ...
I want to use a "generative" approach to defining the set:
0 is in the set.
If i is in the set, then i+2 is in the set.
Nothing else is in the set.
I am struggling with the last one - nothing else is in the set. How do I express that?
Below is the Alloy model that I created.
one sig PositiveEven {
elements: set Int
}
pred generate_set_members {
0 in PositiveEven.elements
all i: Int | i in PositiveEven.elements => i.plus[2] in PositiveEven.elements
// Nothing else is in the set - How to express this?
}
The simplest way to do this would be to create a relationship that maps each number N to N+2, and then take the reflexive-transitive closure of that relationship over 0.
one sig PositiveEven {
elements: set Int
}
one sig Generator {
rel: Int -> Int
} {
all i: Int | i.rel = i.next.next
}
pred generate_set_members {
PositiveEven.elements = 0.*(Generator.rel)
}
assert only_positive_elements {
generate_set_members =>
all i: Int | i in PositiveEven.elements <=> i >= 0 and i.rem[2] = 0
}
Note that you cannot use i.plus[2] instead of i.next.next, because Alloy integers overflow to negative.
What do you think of this:
let iset[min,max,step] = { i : Int |
i>= min
and i<max
and i.minus[min].div[step].mul[step]
= i.minus[min] }
pred show[ s : set Int ] {
iset[ 0, 10, 2 ] = s
}
run show for 0 but 8 int
The visualiser does not show the Int types so look in the Tree or Text view.
I don't understand what to do with the issue reported by the compiler. I tried to create a Range, but it says Index is not known:
//let range = matches.first!.range.location
let range = Range(
start:matches.first!.range.location,
end: matches.first!.range.location+matches.first!.range.length
)
id = text[range]
var t = text
t.removeRange(range)
return t
Compiler says: Cannot invoke 'removeRange' with an argument list of type '(Range)' on t.removeRange(range).
I'm pretty sure it's evident, but I lost a great deal of time on such a small issue… any help highly appreciated!
As your error says that:
Cannot invoke 'removeRange' with an argument list of type '(Range)'
Means there is a problem with your range instance type and removeRange function will only accept an argument with type Range<String.Index> and its syntax is :
/// Remove the indicated `subRange` of characters
///
/// Invalidates all indices with respect to `self`.
///
/// Complexity: O(\ `count(self)`\ ).
mutating func removeRange(subRange: Range<String.Index>)
And here is working example with removeRange:
var welcome = "hello there"
let range = advance(welcome.endIndex, -6)..<welcome.endIndex
welcome.removeRange(range)
println(welcome) //hello
Hope this will help.
Swift 2.2 example of removing first 4 characters:
let range = text.startIndex..<text.startIndex.advancedBy(4)
text.removeRange(range)
That first line feels verbose. I hope newer Swift versions improve upon it.
Here is the working equivalent snippet:
static func unitTest() {
let text = "a👿bbbbb🇩🇪c"
let tag = Tag(id: "🇩🇪")
tag.regex = "👿b+"
print ("Unit test tag.foundIn(\(text)) ? = \(tag.foundIn(text))")
}
func foundIn(text: String) -> (id:String, remainingText:String)? {
// if a regex is provided, use it to capture, and keep the capture as a tag ID
if let regex = regex {
let r = Regex(regex) // text =~ regex
let matches = r.matches(text)
if matches.count >= 1 {
let first = matches.first!.range
let start = advance(text.startIndex, first.location)
let end = advance(start, first.length-1)
let range = Range(start: start, end: end)
id = text[range]
var t = text
t.removeRange(range)
return (id, t)
}
return nil
}
else if let range = text.rangeOfString(id) {
var t = text
t.removeRange(range)
return (id, t)
}
else {
return nil
}
}
The unit test returns :
Unit test tag.foundIn(a👿bbbbb🇩🇪c) ? = Optional(("👿bbbbb", "a🇩🇪c"))
I'd like to convert an Int in Swift to a String with leading zeros. For example consider this code:
for myInt in 1 ... 3 {
print("\(myInt)")
}
Currently the result of it is:
1
2
3
But I want it to be:
01
02
03
Is there a clean way of doing this within the Swift standard libraries?
Assuming you want a field length of 2 with leading zeros you'd do this:
import Foundation
for myInt in 1 ... 3 {
print(String(format: "%02d", myInt))
}
output:
01
02
03
This requires import Foundation so technically it is not a part of the Swift language but a capability provided by the Foundation framework. Note that both import UIKit and import Cocoa include Foundation so it isn't necessary to import it again if you've already imported Cocoa or UIKit.
The format string can specify the format of multiple items. For instance, if you are trying to format 3 hours, 15 minutes and 7 seconds into 03:15:07 you could do it like this:
let hours = 3
let minutes = 15
let seconds = 7
print(String(format: "%02d:%02d:%02d", hours, minutes, seconds))
output:
03:15:07
With Swift 5, you may choose one of the three examples shown below in order to solve your problem.
#1. Using String's init(format:_:) initializer
Foundation provides Swift String a init(format:_:) initializer. init(format:_:) has the following declaration:
init(format: String, _ arguments: CVarArg...)
Returns a String object initialized by using a given format string as a template into which the remaining argument values are substituted.
The following Playground code shows how to create a String formatted from Int with at least two integer digits by using init(format:_:):
import Foundation
let string0 = String(format: "%02d", 0) // returns "00"
let string1 = String(format: "%02d", 1) // returns "01"
let string2 = String(format: "%02d", 10) // returns "10"
let string3 = String(format: "%02d", 100) // returns "100"
#2. Using String's init(format:arguments:) initializer
Foundation provides Swift String a init(format:arguments:) initializer. init(format:arguments:) has the following declaration:
init(format: String, arguments: [CVarArg])
Returns a String object initialized by using a given format string as a template into which the remaining argument values are substituted according to the user’s default locale.
The following Playground code shows how to create a String formatted from Int with at least two integer digits by using init(format:arguments:):
import Foundation
let string0 = String(format: "%02d", arguments: [0]) // returns "00"
let string1 = String(format: "%02d", arguments: [1]) // returns "01"
let string2 = String(format: "%02d", arguments: [10]) // returns "10"
let string3 = String(format: "%02d", arguments: [100]) // returns "100"
#3. Using NumberFormatter
Foundation provides NumberFormatter. Apple states about it:
Instances of NSNumberFormatter format the textual representation of cells that contain NSNumber objects and convert textual representations of numeric values into NSNumber objects. The representation encompasses integers, floats, and doubles; floats and doubles can be formatted to a specified decimal position.
The following Playground code shows how to create a NumberFormatter that returns String? from a Int with at least two integer digits:
import Foundation
let formatter = NumberFormatter()
formatter.minimumIntegerDigits = 2
let optionalString0 = formatter.string(from: 0) // returns Optional("00")
let optionalString1 = formatter.string(from: 1) // returns Optional("01")
let optionalString2 = formatter.string(from: 10) // returns Optional("10")
let optionalString3 = formatter.string(from: 100) // returns Optional("100")
For left padding add a string extension like this:
Swift 5.0 +
extension String {
func padLeft(totalWidth: Int, with byString: String) -> String {
let toPad = totalWidth - self.count
if toPad < 1 {
return self
}
return "".padding(toLength: toPad, withPad: byString, startingAt: 0) + self
}
}
Using this method:
for myInt in 1...3 {
print("\(myInt)".padLeft(totalWidth: 2, with: "0"))
}
Swift 3.0+
Left padding String extension similar to padding(toLength:withPad:startingAt:) in Foundation
extension String {
func leftPadding(toLength: Int, withPad: String = " ") -> String {
guard toLength > self.characters.count else { return self }
let padding = String(repeating: withPad, count: toLength - self.characters.count)
return padding + self
}
}
Usage:
let s = String(123)
s.leftPadding(toLength: 8, withPad: "0") // "00000123"
Swift 5
#imanuo answers is already great, but if you are working with an application full of number, you can consider an extension like this:
extension String {
init(withInt int: Int, leadingZeros: Int = 2) {
self.init(format: "%0\(leadingZeros)d", int)
}
func leadingZeros(_ zeros: Int) -> String {
if let int = Int(self) {
return String(withInt: int, leadingZeros: zeros)
}
print("Warning: \(self) is not an Int")
return ""
}
}
In this way you can call wherever:
String(withInt: 3)
// prints 03
String(withInt: 23, leadingZeros: 4)
// prints 0023
"42".leadingZeros(2)
// prints 42
"54".leadingZeros(3)
// prints 054
Using Swift 5’s fancy new extendible interpolation:
extension DefaultStringInterpolation {
mutating func appendInterpolation(pad value: Int, toWidth width: Int, using paddingCharacter: Character = "0") {
appendInterpolation(String(format: "%\(paddingCharacter)\(width)d", value))
}
}
let pieCount = 3
print("I ate \(pad: pieCount, toWidth: 3, using: "0") pies") // => `I ate 003 pies`
print("I ate \(pad: 1205, toWidth: 3, using: "0") pies") // => `I ate 1205 pies`
in Xcode 8.3.2, iOS 10.3
Thats is good to now
Sample1:
let dayMoveRaw = 5
let dayMove = String(format: "%02d", arguments: [dayMoveRaw])
print(dayMove) // 05
Sample2:
let dayMoveRaw = 55
let dayMove = String(format: "%02d", arguments: [dayMoveRaw])
print(dayMove) // 55
The other answers are good if you are dealing only with numbers using the format string, but this is good when you may have strings that need to be padded (although admittedly a little diffent than the question asked, seems similar in spirit). Also, be careful if the string is longer than the pad.
let str = "a str"
let padAmount = max(10, str.count)
String(repeatElement("-", count: padAmount - str.count)) + str
Output "-----a str"
The below code generates a 3 digits string with 0 padding in front:
import Foundation
var randomInt = Int.random(in: 0..<1000)
var str = String(randomInt)
var paddingZero = String(repeating: "0", count: 3 - str.count)
print(str, str.count, paddingZero + str)
Output:
5 1 005
88 2 088
647 3 647
Swift 4* and above you can try this also:
func leftPadding(valueString: String, toLength: Int, withPad: String = " ") -> String {
guard toLength > valueString.count else { return valueString }
let padding = String(repeating: withPad, count: toLength - valueString.count)
return padding + valueString
}
call the function:
leftPadding(valueString: "12", toLength: 5, withPad: "0")
Output:
"00012"
Details
Xcode 9.0.1, swift 4.0
Solutions
Data
import Foundation
let array = [0,1,2,3,4,5,6,7,8]
Solution 1
extension Int {
func getString(prefix: Int) -> String {
return "\(prefix)\(self)"
}
func getString(prefix: String) -> String {
return "\(prefix)\(self)"
}
}
for item in array {
print(item.getString(prefix: 0))
}
for item in array {
print(item.getString(prefix: "0x"))
}
Solution 2
for item in array {
print(String(repeatElement("0", count: 2)) + "\(item)")
}
Solution 3
extension String {
func repeate(count: Int, string: String? = nil) -> String {
if count > 1 {
let repeatedString = string ?? self
return repeatedString + repeate(count: count-1, string: repeatedString)
}
return self
}
}
for item in array {
print("0".repeate(count: 3) + "\(item)")
}
Unlike the other answers that use a formatter, you can also just add an "0" text in front of each number inside of the loop, like this:
for myInt in 1...3 {
println("0" + "\(myInt)")
}
But formatter is often better when you have to add suppose a designated amount of 0s for each seperate number. If you only need to add one 0, though, then it's really just your pick.
My question is how can I get values of enum variable?
Please look at the attached screenshot... "hatas" is a flag-enum. And I want to
get "HasError" - "NameOrDisplayNameTooShort" errors to show them.
using System;
namespace CampaignManager.Enums
{
[Flags]
public enum CampaignCreaterUpdaterErrorMessage
{
NoError = 0,
HasError = 1,
NameOrDisplaynameTooShort = 2,
InvalidFirstName = 3,
}
}
I tried simply;
Messagebox.Show(hatas); // it's showing InvalidFirstName somehow...
Thank you very much for any help...
First thing: If you want to use the FlagsAttribute on your enum you need to define the values in powers of two like this:
[Flags]
public enum CampaignCreaterUpdaterErrorMessage
{
NoError = 0,
HasError = 1,
NameOrDisplaynameTooShort = 2,
InvalidFirstName = 4,
}
To get parts of a flagged enum, try something like:
var hatas = CampaignCreaterUpdaterErrorMessage.HasError | CampaignCreaterUpdaterErrorMessage.NameOrDisplaynameTooShort;
var x = (int)hatas;
for (int i=0; i<Enum.GetNames(typeof(CampaignCreaterUpdaterErrorMessage)).Length; i++)
{
int z = 1 << i; // create bit mask
if ((x & z) == z) // test mask against flags enum
{
Console.WriteLine(((CampaignCreaterUpdaterErrorMessage)z).ToString());
}
}
For getting the underlying value try casting:
Messagebox.Show(((int)hatas)ToString());
In your example, ToString is getting called by default against the CampaignCreaterUpdaterErrorMessage enum which return the string representation of the enum.
By casting to an int, the underlying default type for enums, you get ToString on the integer value.
You need to cast/unbox the enum into an int as follows.
(int)CampaignCreaterUpdaterErrorMessage.NoError
(int)CampaignCreaterUpdaterErrorMessage.HasError
Try this:
Messagebox.Show(CampaignCreaterUpdaterErrorMessage.NameOrDisplaynameTooShort);