我正在尝试创建一个遵循Bodmas规则的计算器，并首先尝试使用乘法。当按下equals按钮时，诸如“ 4 * 5 + 6 * 7”之类的字符串将存储在displayValue中。 第一次尝试使用reg ex在字符串中搜索乘法符号及其位置。当它找到lhs和rhs的值并将其存储时进行校准。然后，它使用firstValue，secValue乘以值，并将cal替换为displayValue中的结果。这适用于4 * 5，但我必须再次按equals才能执行6 * 7。我尝试使用while循环，但无法正常工作。如何一次性完成字符串中的所有乘法部分？
equals() {
const displayValue = this.state.displayValue.slice(0);
let counter = displayValue.match(/[\d\.]+(?=\*)\*[\d\.]+/g).length;
console.log("counter: " +counter);
while (counter > 0) {
let cal = displayValue.match(/[\d\.]+(?=\*)\*[\d\.]+/).toString().split("*").join(",");
console.log("cal: " +cal)
let operPos = cal.search(/\*/);
let firstValue = parseFloat(cal.slice(0, operPos));
let secValue = parseFloat(cal.slice(operPos + 1));
let finalCal = firstValue * secValue;
let result = displayValue.replace(/[\d\.]+(?=\*)\*[\d\.]+/, finalCal);
this.setState({displayValue: result});
counter = counter -1;
console.log("counterII: " +counter)
}
console.log("new display: " +this.state.displayValue)
}
答案 0 :(得分：0)
displayValue在每个循环中都没有更新，因为我将其分配为const变量。这是正确的代码：
equals() {
let displayValue = this.state.displayValue.slice(0);
let counter = displayValue.match(/[\d\.]+(?=\*)\*[\d\.]+/g).length;
console.log("counter: " +counter);
while (counter > 0) {
let cal = displayValue.match(/[\d\.]+(?=\*)\*[\d\.]+/).toString().split("*").join(",");
console.log("cal: " +cal)
let operPos = cal.search(/\*/);
let firstValue = parseFloat(cal.slice(0, operPos));
let secValue = parseFloat(cal.slice(operPos + 1));
let finalCal = firstValue * secValue;
displayValue = displayValue.replace(/[\d\.]+(?=\*)\*[\d\.]+/, finalCal);
this.setState({displayValue: displayValue})
console.log("result: " +displayValue)
counter = counter -1;
console.log("counterII: " +counter)
}
}
如果有人有更好的方法实现同一目标，请告诉我。
答案 1 :(得分：0)
为什么不使用eval()操作？例如：
document.getElementById("clickMe").onclick = function(){
let foo = eval("2*4*2");
console.log(foo);//16
return;
}<button id="clickMe">Click for Demo</button>
有时它甚至也可以解析function！
编辑：该答案不再有效，因为询问者打算逐步进行BEDMAS。
但是，我将其留在这里供以后的读者使用。
答案 2 :(得分：0)
我已经使用JavaScript创建了一个基于BODMAS的计算器
对于完整项目：
// +++++++++++++++++ //
// Sample Test Cases //
// +++++++++++++++++ //
// 10+20-30+40*5/2+10/5
// 10*20-30/40/5+2-10*5*9
// 10*20-30/40*5/2-10*5*0
// 10+20-30+40*5/2+10*5/5
// 10*20-30/40*5/2-10*5-87*2+115*111
// 10+20-30+40*5/(2+10*5)*5
// 10+20-(30+40)*5/2+(10*5)/5+(6+9)
// 10+20-(30+40*(10+10))*5/2+(10*5)/5+(6+9)
// 10+20-((30+40)*(10+10))*5/2+(10*5)/5+(6+9)
// ((14+11)+15*16-(13+10*11)+(10+10-(10*2)))
// 10+20-((30+40)*10+(10+(10*5))+10)
// 10+20-((30+40)*10+(10+(10*5+9)+9))+10
// 10+20-((30+40)*10+(10+(10+5))+10/(5*(10+10)))*5/2+(10*5)/5+(6+9+78/7)
// (10+20)-((30+40)*10+(10+(10+5)-(5+5))+(10/(5*(10+10)))*5/2+(10*5)/5+(6+9+78/7))
/// 10*(20-30/2)+40*5+2-(10*5+9)-(87*2+115*111)
/// 10*(20-30/2)+40*5+2-(10*5+9)*1-(87*2+115*111)
// console.log(eval(10*(20-30/2)+40*5+2-(10*5+9)-(87*2+115*111)))
function append(text) {
document.getElementById("equation").value += text
}
function clearEquation() {
document.getElementById("equation").value = ""
document.getElementById("result").value = ""
}
function backspace(text) {
document.getElementById("equation").value = text.substring(0, text.length - 1)
}
function startEvaluation(equation) {
console.log(eval(equation))
// var equation = prompt("Enter the equation")
// Creating empty arrays for storing
// brackets, operators, operands
var brackets = []
var operators = []
var operands = []
var operandString = ""
for (var index = 0, operatorIndex = 0, bracketIndex = 0; index < equation.length; index++) {
// Checking for operators
if (equation.charAt(index) == '+'
|| equation.charAt(index) == '-'
|| equation.charAt(index) == '*'
|| equation.charAt(index) == '/') {
// Below condition is to deal with (a+b)+(c+d) this part of equation
if (equation.charAt(index - 1) == ')' && equation.charAt(index + 1) == '(') {
operators[operatorIndex++] = "*"
brackets[bracketIndex++] = null
brackets[bracketIndex++] = null
operators[operatorIndex++] = equation.charAt(index)
operandString += " 1 "
}
// Fetching operators and storing into operators[] array
else {
operators[operatorIndex++] = equation.charAt(index)
brackets[bracketIndex++] = null
operandString += " "
}
}
// Fetching brackets and storing into brackets[] array
else if (equation.charAt(index) == '(' || equation.charAt(index) == ')') {
brackets[bracketIndex++] = equation.charAt(index)
operators[operatorIndex++] = null
}
// Fetching operand digits and storing into operandString
else {
operandString += equation.charAt(index)
}
}
// Temp array of operands for further processing
// before storing operands into operands[] array
operandsTemp = operandString.split(" ")
// Storing operands into operands[] array
for (var index = 0, indexOperand = 0; index < operators.length; index++) {
if (brackets[index] == null) {
operands[index] = Number(operandsTemp[indexOperand++])
}
else {
operands[index] = null
}
}
operands[operands.length] = Number(operandsTemp[indexOperand])
console.log(brackets)
console.log(operators)
console.log(operands)
// Result variables
var result = 0
var finalResult = 0
// Checking if brackets are present in the equation or not
if (brackets.length > 0) {
for (var index = 0; index < brackets.length; index++) {
// Checking for occurance of closing bracket
// and then searching for its corresponding
// opening bracket by reverse traversing
// and then evaluating that particular bracket equation
// PROCESSES NESTED BRACKETS AS WELL
if (brackets[index] == ')') {
var indexBracketEnd = index
for (var indexBracket = indexBracketEnd; indexBracket >= 0; indexBracket--) {
if (brackets[indexBracket] == '(') {
var indexBracketStart = indexBracket
evaluate(indexBracketStart, indexBracketEnd, operators, operands)
brackets[indexBracketStart] = null
brackets[indexBracketEnd] = null
break
}
}
console.log(brackets)
}
}
}
// This will evaluate remaining equation (without brackets)
// after processing brackets (if available)
finalResult = evaluate(0, operators.length, operators, operands)
// FINAL RESULT
console.log(`FINAL RESULT = ${finalResult}`)
document.getElementById('result').value = finalResult
}
// Evaluation of equation by using BOAD MASS method
function evaluate(indexStart, indexEnd, operators, operands) {
// First evaluating MULTIPLICATION and DIVISION
for (var index = indexStart; index < indexEnd; index++) {
var indexFirstOperand = index
var indexNextOperand = index + 1
var indexNextOperator = index
if (operators[indexNextOperator] == null) {
for (var indexNext = indexNextOperator + 1; indexNext < operators.length; indexNext++) {
if (operators[indexNext] != null) {
indexNextOperator = indexNext
indexFirstOperand = indexNext
indexNextOperand = indexNext + 1
index = indexNext - 1
break
}
}
}
if (operands[indexNextOperand] == null) {
for (var indexNext = indexNextOperand + 1; indexNext < operands.length; indexNext++) {
if (operands[indexNext] != null) {
indexNextOperand = indexNext
index = indexNext - 1
break
}
}
}
// MULTIPLICATION
if (operators[indexNextOperator] == '*') {
result = operands[indexFirstOperand] * operands[indexNextOperand]
operands[indexNextOperand] = result
operands[indexFirstOperand] = null
operators[indexNextOperator] = null
finalResult = result
result = 0
console.log(operands)
console.log(operators)
}
// DIVISION
else if (operators[indexNextOperator] == '/') {
result = operands[indexFirstOperand] / operands[indexNextOperand]
operands[indexNextOperand] = result
operands[indexFirstOperand] = null
operators[indexNextOperator] = null
finalResult = result
result = 0
console.log(operands)
console.log(operators)
}
}
// Next evaluating ADDITION and SUBSTRACTION
for (var index = indexStart; index < indexEnd; index++) {
var indexFirstOperand = index
var indexNextOperand = index + 1
var indexNextOperator = index
if (operators[indexNextOperator] == null) {
for (var indexNext = indexNextOperator + 1; indexNext < operators.length; indexNext++) {
if (operators[indexNext] != null) {
indexNextOperator = indexNext
indexFirstOperand = indexNext
indexNextOperand = indexNext + 1
index = indexNext - 1
break
}
}
}
if (operands[indexNextOperand] == null) {
for (var indexNext = indexNextOperand + 1; indexNext < operands.length; indexNext++) {
if (operands[indexNext] != null) {
indexNextOperand = indexNext
index = indexNext - 1
break
}
}
}
// ADDITION
if (operators[indexNextOperator] == '+') {
result = operands[indexFirstOperand] + operands[indexNextOperand]
operands[indexNextOperand] = result
operands[indexFirstOperand] = null
operators[indexNextOperator] = null
finalResult = result
result = 0
console.log(operands)
console.log(operators)
}
// SUBSTRACTION
else if (operators[indexNextOperator] == '-') {
result = operands[indexFirstOperand] - operands[indexNextOperand]
operands[indexNextOperand] = result
operands[indexFirstOperand] = null
operators[indexNextOperator] = null
finalResult = result
result = 0
console.log(operands)
console.log(operators)
}
}
// Returning FINAL RESULT
return finalResult
}