[英]How can I extract numbers from string in Swift in a specific way
我正在努力從 Swift 中的字符串中提取數字。 我正在執行以下操作:
let expression: String = "abc123aa223bb45"
for (indx, ch) in expression.enumerated() {
if ch.isLetter { continue }
else if ch.isNumber {
var val: Int = 0
while(indx < expression.count && ch.isNumber){
val = val * 10 + (ch.asciiValue - 48)
//how can I proceed and increment both indx and ch ...
}
// here I'm going to do smthing with every extracted number
}
}
有人可以幫我完成我遇到的這個問題嗎?
我也使用擴展
extension Character {
var asciiValue: Int {
get {
let s = String(self).unicodeScalars
return Int(s[s.startIndex].value)
}
}
}
正如您在發布的代碼片段中看到的那樣
我正在嘗試編寫一個使用大括號和運算符評估表達式的程序:^,+,-,/,*
但是我遇到了一些問題(我已經用 C++ 和 C# 做過很多次,但我無法用 swift 做到這一點。這真的讓我非常頭疼:)
import Foundation
extension Character {
var asciiValue: Int {
get {
let s = String(self).unicodeScalars
return Int(s[s.startIndex].value)
}
}
}
precedencegroup PowerPrecedence { higherThan: MultiplicationPrecedence }
infix operator ^^ : PowerPrecedence
func ^^ (radix: Double, power: Int) -> Double {
return (pow(Double(radix), Double(power)))
}
func calc(a: Double, b: Double, o: Character) -> Double {
switch o {
case "+":
return a + b
case "-":
return a - b
case "/":
return a / b
case "*":
return a * b
case "^":
return a ^^ Int(b)
default:
return 0
}
}
func nice(o: Character) -> Int {
if o == "-" || o == "+" { return 1 }
if o == "*" || o == "/" { return 2 }
if o == "^" { return 3 }
return 2020
}
func evaluate(expression: String) -> Double {
var vals = [Double]()
var ops = [Character]()
for (indx, ch) in expression.enumerated() {
if ch == " " { continue }
else if ch == "(" { ops.append(ch) }
else if ch.isNumber {
var val: Int = 0
while(indx < expression.count && ch.isNumber){
val = val * 10 + ch.asciiValue - 48 // gives strange error
//TODO increment indx and ch
}
vals.append(Double(val))
} else if ch == ")" {
while !ops.isEmpty && ops.last != "(" {
let val_2: Double = vals.popLast()!
let val_1: Double = vals.popLast()!
let op: Character = ops.popLast()!
vals.append(calc(a: val_1, b: val_2, o: op))
}
if !ops.isEmpty { _ = ops.popLast() } // opening brace
} else {
while(!ops.isEmpty && nice(o: ops.last!) >= nice(o: ch)){
let val_2: Double = vals.popLast()!
let val_1: Double = vals.popLast()!
let op: Character = ops.popLast()!
vals.append(calc(a: val_1, b: val_2, o: op))
}
ops.append(ch);
}
}
while !ops.isEmpty {
let val_2: Double = vals.popLast()!
let val_1: Double = vals.popLast()!
let op: Character = ops.popLast()!
vals.append(calc(a: val_1, b: val_2, o: op))
}
return vals.last!
}
let exp: String = "2^3+(2+3)"
print(evaluate(expression: exp))
以下代碼片段將從字符串中提取數字
let expression: String = "abc123aa223bb45"
let stringArray = expression.components(separatedBy: CharacterSet.decimalDigits.inverted)
for item in stringArray {
if let number = Int(item) {
print(number)
}
}
您還可以對具有 function 的 Int 進行擴展
extension Int {
static func parse(from string: String) -> Int? {
return Int(string.components(separatedBy: CharacterSet.decimalDigits.inverted).joined())
}
}
可以這樣使用
let expression: String = "abc123aa223bb45"
if let number = Int.parse(from: expression) {
print(number)
}
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