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Calculator.swift
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Calculator.swift
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/*Create a simple calculator and calculate the values based on the order of precedence
Input will be string (e.g., "(2*3)+3*5")
Here the evaluation will happen based on precedence order as = (2*3)+3*5
= 6+3*5
= 6+15
= 21 */
import Foundation
let expression = Array("22.2+3".replacingOccurrences(of: " ", with: "")) //remove the whitespaces
let symbolsArray = ["+","-","*","/","(",")","^"]
//convert infix to postfix
func performArithmeticCalculationByConvertingInfixToPostfix(for infixExpression: [Character]) -> Double {
var precedence = ["*": 3, "/": 3, "+": 2, "-": 2, "(": 1]
var operatorList: [String] = [] //store operators
var postfixList: [String] = [] //store numbers
let expressionList: [String] = Array(createExpressionList(for: infixExpression)) //calls function to separate the expression correctly
for each in expressionList {
if symbolsArray.contains(each) != true {
postfixList.append(each)
}
else if each == "(" {
operatorList.append(each)
}
else if each == ")" {
var removedElement = operatorList.removeLast()
while "\(removedElement)" != "(" {
postfixList.append(removedElement)
removedElement = operatorList.removeLast()
}
}
else {
while operatorList.count != 0 && precedence[operatorList.last!]! >= precedence[each]! {
postfixList.append(operatorList.removeLast())
}
operatorList.append(each)
}
}
while operatorList.count != 0 {
postfixList.append(operatorList.removeLast())
}
return postfixEvaluation(for: postfixList)
}
//creating infixExpression
func createExpressionList(for infixExpression: [Character]) -> [String] {
var temporaryValue = 0
var infixExpression = Array(infixExpression)
var flag = 0
var index = 0
var expressionList: [String] = []
while index < infixExpression.count {
var startingIndex = 0
if index < infixExpression.count - 1 {
if infixExpression[index + 1] == "." && symbolsArray.contains(String(infixExpression[index])) != true || infixExpression[index] == "."{
startingIndex = index
while index < infixExpression.count - 1 {
if symbolsArray.contains(String(infixExpression[index])) != true {
index += 1
}
else if symbolsArray.contains(String(infixExpression[index])) {
index -= 1
break
}
else {
index += 1
break
}
}
if flag == 1 {
temporaryValue *= 10
temporaryValue += Int(String(infixExpression[startingIndex])) ?? 0
let temporaryString = String(temporaryValue) + String(infixExpression[startingIndex + 1...index])
expressionList.append(temporaryString)
temporaryValue = 0
flag = 0
}
else {
expressionList.append(String(infixExpression[startingIndex...index]))
}
}
else if symbolsArray.contains(String(infixExpression[index])) != true {
temporaryValue *= 10
temporaryValue += (Int(String(infixExpression[index])) ?? 0)
flag = 1
}
else {
if flag == 1 {
expressionList.append(String(temporaryValue))
}
if infixExpression[index] == "(" && index != 0 {
if symbolsArray.contains(String(infixExpression[index - 1])) != true {
expressionList.append("*")
}
}
expressionList.append(String(infixExpression[index]))
if infixExpression[index] == ")" && index < infixExpression.count {
if infixExpression[index + 1] == "(" || symbolsArray.contains(String(infixExpression[index + 1])) != true{
expressionList.append("*")
}
}
temporaryValue = 0
flag = 0
}
}
else {
if index <= infixExpression.count - 1 {
if flag == 1 && symbolsArray.contains(String(infixExpression[index])) {
expressionList.append(String(temporaryValue))
expressionList.append(String(infixExpression[index]))
}
else if flag == 1 {
temporaryValue = temporaryValue * 10 + (Int(String(infixExpression[index])) ?? 0)
expressionList.append(String(temporaryValue))
}
else {
expressionList.append(String(infixExpression[index]))
}
}
}
index = index + 1
}
return expressionList
}
//evaluation of postfix expression
func postfixEvaluation(for postfixExpression: [String]) -> Double {
var operandList: [Double] = []
let symbols: [String] = ["+","-","*","/","(",")","."]
let symbolsBasedValues = ["+": 0.0, "-": 0.0, "*": 1.0, "/": 1.0]
var result = 0.0
for each in postfixExpression {
if symbols.contains(each) != true {
operandList.append(Double(String(each)) ?? 0)
}
else {
if operandList.count == 1 {
result = performArithmeticOperation(of: each, for: operandList.removeLast(),and: symbolsBasedValues[each]!)
}
else {
result = performArithmeticOperation(of: each, for: operandList.removeLast(),and: operandList.removeLast())
}
operandList.append(result)
}
}
return operandList.removeLast()
}
//perform calculations based on operators
func performArithmeticOperation(of operators: String,for secondOperand: Double,and firstOperand: Double) -> Double {
switch operators {
case "+" :
return firstOperand + secondOperand
case "-" :
return firstOperand - secondOperand
case "*" :
return firstOperand * secondOperand
case "/" :
return firstOperand / secondOperand
default :
return 0
}
}
let finalResult: Double = performArithmeticCalculationByConvertingInfixToPostfix(for: expression)
print(String(expression) + "=" + "\(finalResult)")