def guessing_game():Unit = {
println("Welcome to the guessing game!!")
val guess_count:Int = 0
val answer = Random.nextInt(50)
var guess_num = scala.io.StdIn.readLine("Input your guess number > ").toInt
while(guess_num != answer || guess_count < 5){
====> guess_count += 1 // <==============================
var situation = if(guess_num > answer){"Your guess is higher!"}else{"Your guess is lower!"}
println(situation)
guess_num = scala.io.StdIn.readLine("Input your guess number > ").toInt
}
if(guess_num == answer){
println("Congratulation....You win!!")
}else{
println("You hav run out of guess!")
}
It says:
Error:(16, 25) value += is not a member of Int
Expression does not convert to assignment because receiver is not assignable.
guess_count.toInt += 1
guess_count is immutable, (val), you cannot change it. Use var if you need to change the variable.
you can increment in scala, but the wrong is you are incrementing and re assigning the value to a final variable, that's why it's throwing error, please change the declaration as below then it will work
var guess_count:Int = 0
Thanks
Related
I created a function that recieves input and compare it to a list, when find a match it return the match, in this case this match is the attribute of a class that i created.
I understand that the problem is with the return statement, so in the beginning of the function I declare the return as "Any", further more than that I'm kinda lost.
The error is this: A 'return' expression required in a function with a block body ('{...}')
class Class1(var self: String)
var test_class = Class1("")
fun giver(){
test_class.self = "Anything"
}
class Funciones(){
fun match_finder(texto: String): Any{
var lista = listOf<String>(test_class.self)
var lista_de_listas = listOf<String>("test_class.self")
var count = -1
for (i in lista_de_listas){
count = count + 1
if (texto == i){
lista_de_listas = lista
var variable = lista_de_listas[count]
return variable
}
}
}
}
fun main(){
giver()
var x = "test_class.self"
var funcion = Funciones()
var y = funcion.match_finder(x)
println(y)
}
To explain you what the problem is, let's consider the following code:
class MyClass {
fun doSomething(): String {
val numbers = listOf(1, 2, 3)
for (number in numbers) {
if (number % 2 == 0) {
return "There is at least one even number in the list"
}
}
}
}
If you try compiling it you'll get the same error message as in your question: A 'return' expression required in a function with a block body ('{...}'). Why is that?
Well, we defined a function doSomething returning a String (it could be any other type) but we're returning a result only if the list of numbers contains at least one even number. What should it return if there's no even number? The compiler doesn't know that (how could it know?), so it prompts us that message. We can fix the code by returning a value or by throwing an exception:
class MyClass {
fun doSomething(): String {
val numbers = listOf(1, 2, 3)
for (number in numbers) {
if (number % 2 == 0) {
return "There is at least one even number in the list"
}
}
// return something if the list doesn't contain any even number
return "There is no even number in the list"
}
}
The same logic applies to your original code: what should the function return if there is no i such that texto == i?
Please also note that the solution you proposed may be syntactically correct - meaning it compiles correctly - but will probably do something unexpected. The for loop is useless since the if/else statement will always cause the function to return during the first iteration, so the value "There is no match" could be returned even if a match actually exists later in the list.
I searched online, if someone has the same problem, the correct code is as follows:
class Funciones(){
fun match_finder(texto: String): Any{
var lista = listOf<String>(test_class.self)
var lista_de_listas = listOf<String>("test_class.self")
var count = -1
var variable = " "
for (i in lista_de_listas){
count = count + 1
if (texto == i){
lista_de_listas = lista
var variable = lista_de_listas[count]
return variable
} else {
return "There is no match"
}
}
return variable
}
}
I'm trying to write a function that has arrayOne, arrayTwo, and arrayThree as inputs. If arrayTwo has any 0s as its last elements, the function is supposed to remove these elements from the array, as well as the same elements from arrayOne. When I run the code and try to test it, I get the error: "Terminated by signal 4".
What could the problem be?
var arrayOneNew = arrayOne
var arrayTwoNew = arrayTwo
var arrayThreeNew = arrayThree
var endElement = arrayTwoNew.last
if endElement == 0 {
var counter = arrayTwoNew.count
while arrayTwoNew[counter] == 0 {
var elementToBeRemoved = arrayTwoNew.remove(at: counter - 1)
var 2ndElementToBeRemoved = arrayOneNew.remove(at: counter - 1)
}
}
Your main problem is that you are setting counter to arrayTwoNew.count which is 1 bigger than the last valid index in arrayTwoNew, so while arrayTwoNew[counter] == 0 crashes with index out of range.
Also:
var elementToBeRemoved = arrayTwoNew.remove(at: counter - 1)
is probably meant to remove the last item from arrayTwoNew, but that is more easily accomplished with:
arrayTwoNew.removeLast()
especially since you're not using elementToBeRemoved.
I think you're trying to do this:
while arrayTwoNew.last == 0 {
arrayTwoNew.removeLast()
arrayOneNew.removeLast()
arrayThreeNew.removeLast()
}
You are creating a new array "arrayTwoNew" which is mixed up with the original one at
var arrayTwoNew = arrayTwoNew.remove(at: counter - 1)
Now I'm also struggling with your .remove - this returns an element so won't work. I'd usually use a filter here but I'm not sure what you are doing!
//code with remove taken out (replace with filter?) to get you started:
let arrayOne = [1,2,3]
let arrayTwo = [2,3,4]
let arrayThree = [5,6,7]
var arrayOneNew = arrayOne
var arrayTwoNew = arrayTwo
var arrayThreeNew = arrayThree
var endIndex = arrayTwoNew.last
if endIndex == 0 {
let counter = arrayTwoNew.count
// arrayTwoNew = arrayTwoNew.remove(at: counter - 1)
while arrayTwoNew[counter] == 0 {
// arrayOneNew = arrayOneNew.remove(at: counter - 1)
}
}
I have an issue with my n variable. I cannot use n in for loop. Why? n was initialized before for loop. Please, help.
import Foundation
var n: Int
var t: Int
while(true){
var tt = readLine()
t = Int(tt!)!
if (t==0){
break
}
else if ( t < 0){
n = t*(-1)
}
else if(t > 0){
n = t
}
var arr : [[String]] = []
for i in 0..<n*2{
for y in 0..<n*2{
arr[i][y] = "."
}
}
}
A variable may be declared and not immediately initialized, as long as initialization is guaranteed before first use
The error is more subtle than at first glance. You may actually declare a property without initializing it, as long as all program flows leading to its first use ascertain initialization of it.
The issue is with the if, else if and else if block:
var n: Int // declaration
// ...
if (t == 0) {
break
}
else if (t < 0) {
n = t*(-1)
}
else if (t > 0){
n = t
}
// first use
for i in 0..<n*2 { /* ... */ }
Swift cannot not infer that this block is in fact exhaustive, and believes that there is a possibility that none of the above if statements holds, which, in the eyes of the compiler, would lead to the following program state:
program flow has not been broken (break)
and n has not been instantiated
As humans, however, we know that the if - else if - else if block above is indeed exhaustive, and can help the compiler out by simply changing the last if else statement to a simple else statement.
if (t == 0) {
break
}
else if (t < 0) {
n = t*(-1)
}
// if none of the above, t > 0
else {
n = t
}
On another note, the nested array access of non-existing array elements, arr[i][y] = "." will lead to a runtime exception, but this is another issue. In its current form, it looks as if the intent with the nested loops could be replaced with a nested array instantiation:
var arr = [[String]](repeating: [String](repeating: ".", count: 2*n), count: 2*n)
or,
var arr = (0..<2*n).map { _ in [String](repeating: ".", count: 2*n) }
The variable n is only declared, not initialized.
To initialize the variables:
var n: Int = 0
var t: Int = 0
I'm currently converting C++ code to Swift and I've gotten stuck on one part. The parameter passed into the function is a string and the area where I'm stuck is when attempting to set a variable based on the second to last character of a string to check for a certain character.
The error shows up on this line:
line[i-1]
I've tried casting this value to an Int but this didn't work:
Int(line[i - 1])
I've also tried to see if the string's startIndex function which takes a Int would work but it didn't:
line.startIndex[i - 1]
Here is the full function:
func scanStringForSpecificCharacters(line: String){
var maxOpen: Int = 0;
var minOpen: Int = 0;
minOpen = 0;
maxOpen = 0;
var i = 0
while i < line.characters.count {
for character in line.characters {
//var c: Character = line[i];
if character == "(" {
maxOpen += 1;
if i == 0 || line[i - 1] != ":" {
minOpen += 1;
}
}
else if character == ")"{
minOpen = max(0,minOpen-1);
if i == 0 || line[i-1] != ":"{
maxOpen -= 1;
}
if maxOpen < 0{
break;
}
}
}
if maxOpen >= 0 && minOpen == 0{
print("YES")
}else{
print("NO")
}
}
}
Strings in Swift aren't indexed collections and instead you can access one of four different views: characters, UTF8, UTF16, or unicodescalars.
This is because Swift supports unicode, where an individual characters may actually be composed of multiple unicode scalars.
Here's a post that really helped me wrap my head around this: https://oleb.net/blog/2016/08/swift-3-strings/
Anyway, to answer you question you'll need to create an index using index(after:), index(before:), or index(_, offsetBy:).
In your case you'd want to do something like this:
line.index(line.endIndex, offsetBy: -2) // second to last character
Also, you'll probably find it easier to iterate directly using a String.Index type rather than Int:
let line = "hello"
var i = line.startIndex
while i < line.endIndex {
print(line[i])
i = line.index(after: i)
}
// prints ->
// h
// e
// l
// l
// o
Working with Strings in Swift was changed several times during it's evolution and it doesn't look like C++ at all. You cannot subscript string to obtain individual characters, you should use index class for that. I recommend you read this article:
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html
As already pointed out in the other answers, the compiler error
is caused by the problem that you cannot index a Swift String with
integers.
Another problem in your code is that you have a nested loop which is
probably not intended.
Actually I would try to avoid string indexing at all and only
enumerate the characters, if possible. In your case, you can
easily keep track of the preceding character in a separate variable:
var lastChar: Character = " " // Anything except ":"
for char in line.characters {
if char == "(" {
maxOpen += 1;
if lastChar != ":" {
minOpen += 1;
}
}
// ...
lastChar = char
}
Or, since you only need to know if the preceding character is
a colon:
var lastIsColon = false
for char in string.characters {
if char == "(" {
maxOpen += 1;
if !lastIsColon {
minOpen += 1;
}
}
// ...
lastIsColon = char == ":"
}
Another possible approach is to iterate over the string and a shifted
view of the string in parallel:
for (lastChar, char) in zip([" ".characters, line.characters].joined(), line.characters) {
// ...
}
As others have already explained, trying to index into Swift strings is a pain.
As a minimal change to your code, I would recommend that you just create an array of the characters in your line up front:
let linechars = Array(line.characters)
And then anywhere you need to index into the line, use linechars:
This:
if i == 0 || line[i-1] != ":" {
becomes:
if i == 0 || linechars[i-1] != ":" {
In Swift, I need to create a simple for-condition-increment loop with all the multiples of 3 from 3-100. So far I have:
var multiplesOfThree: [String] = []
for var counter = 0; counter < 30; ++counter {
multiplesOfThree.append("0")
if counter == 3 {
multiplesOfThree.append("3")
} else if counter == 6 {
multiplesOfThree.append("6")
} else if counter == 9 {
multiplesOfThree.append("9")
}
println("Adding \(multiplesOfThree[counter]) to the Array.")
}
I would like to replace all the if and else if statements with something like:
if (index %3 == 0)
but I’m not sure what the proper syntax would be? Also, if I have a single IF statement do I need a .append line to add to the Array?
You are very much on the right track. A few notes:
Swift provides a more concise way to iterate over a fixed number of integers using the ..< operator (an open range operator).
Your if statement with the modulus operator is exactly correct
To make a string from an Int you can use \(expression) inside a string. This is called String Interpolation
Here is the working code:
var multiplesOfThree: [String] = []
for test in 0..<100 {
if (test % 3 == 0) {
multiplesOfThree.append("\(test)")
}
}
However, there is no reason to iterate over every number. You can simply continue to add 3 until you reach your max:
var multiplesOfThree: [String] = []
var multiple = 0
while multiple < 100 {
multiplesOfThree.append("\(multiple)")
multiple += 3
}
As rickster pointed out in the comments, you can also do this in a more concise way using a Strided Range with the by method:
var multiplesOfThree: [String] = []
for multiple in stride(from: 0, to: 100, by: 3) {
multiplesOfThree.append("\(multiple)")
}
Getting even more advanced, you can use the map function to do this all in one line. The map method lets you apply a transform on every element in an array:
let multiplesOfThree = Array(map(stride(from: 0, to: 100, by: 3), { "\($0)" }))
Note: To understand this final code, you will need to understand the syntax around closures well.