BODMAS系统的加法和减法 [英] adding and subtracting for BODMAS system

问题描述

我一直在构建一个简单的公式计算器，并被加法和减法所困扰.如您所知，在计算方程式时，请遵循优先级的算术规则，即方括号，顺序:幂函数，除法，乘法，加法和减法.问题是加法和减法具有相同的优先级，因此您可以从左到右读取它.到目前为止，这是我的代码:

I have been building a simple formula calculator and have gotten stuck with addition and subtraction. As you should know, when calculating an equation, you follow the arithmetic rules of precedence, i.e. brackets, order: power functions, division, multiplication, addition and subtraction. The problem is that addition and subtraction are given equal priority, so therefore you can read it from left to right. Here is my code so far:

{
ArrayList<String> equation = java.util.Arrays.asList({"2","-","2","+","5"});

  while(equation.contains("+")){
          addMe(equation);
  }
  while(equation.contains("-")){
          minusMe(equation);            
  }
}

public static void addMe(ArrayList<String> numberList){
 for (int i = 0, n = numberList.size(); i < n; i++) { 
   String value = (String) numberList.get(i); 
   if(value.equals("+")){

    String wordBefore = (String) numberList.get(i-1);
    String wordAfter = (String) numberList.get(i+1);
    System.out.println("This is the word before " + wordBefore);
    System.out.println("This is the word after " + wordAfter);
    double doubleFromBefore = Double.parseDouble(wordBefore);
    double doubleFromAfter = Double.parseDouble(wordAfter);
    double answer = doubleFromBefore + doubleFromAfter;
    System.out.println("This is the answer: " + answer);
    String stringAnswer = String.valueOf(answer);
    String newNum2 = value.replace(value, stringAnswer);
    numberList.set(i,newNum2);
    numberList.remove(i-1);
    numberList.remove(i);
    break;
  }
 }   
}

minusMe方法与addMe方法完全相同，只不过在相关位置带有-".我遇到的问题是一次从左到右读取方程式，然后执行加法或减法.理想情况下，我认为我需要将2个while循环与一个迭代器结合起来以解决问题，但我的尝试没有用.有什么想法可以解决我的问题吗?如果是这样，请提供修改后的循环.

The minusMe method is exactly the same as the addMe method except with "-" in relevant places. The problem I am having is getting the equation read from left to right one item at a time and either doing the add or subtract method. Ideally I think I need to combine my 2 while loops with an iterator, to solve the problem but my attempts haven't worked. Any idea as to if this will solve my problem? If so please provide amended loop.

致谢

推荐答案

看看这个

java.uti.ArrayList<String> equation = java.util.Arrays.asList({"2","-","2","+","5"});
java.util.Iterator<String> equIterator = equation.iterator();
int result = 0;
int multiplier = 1;
while(equIterator.hasNext()){
     String operandOrOperator = equIterator.next();
     if(operandOrOperator.equals("+")){
          multiplier=1;
     }else if(operandOrOperator.equals("-")){
          multiplier=-1;
     }else if(operandOrOperator.equals("*")){
          result*=Integer.parseInt(equIterator.next()); // Assuming that next element will be there always after operator.
     }else{
          result+=(multiplier * Integer.parseInt(operandOrOperator));
     }
}
System.out.println("Final result : " + result);

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