int形式的字符串方程式答案

问题描述：

我在一个低级别的java类中，我需要使用java和JavaScript制作应用程序。我决定创建一个使用加法，减法，乘法和除法创建随机方程的游戏。我遇到的麻烦是我的等式是以字符串的形式创建的，我需要能够计算答案以将其与用户答案进行比较。我认为我有一个解决我的问题的后裔解决方案，但我不断收到一些问题。你能帮我吗？我的代码如下：int形式的字符串方程式答案

import java.util.*; 
public class GameClient { 

    private static Stack<String> operations; 
    private static Stack<Integer> numbers; 
    private static String[] tokens; 
    private static int i; 
    private static Stack<String> subAdd; 
    private static Stack<Integer> restOfNumbers; 

    public static void main(String[] args) { 
     Random variable = new Random(); 
     int numberOfVariables = variable.nextInt(5)+2;  //determines length of equation 
     String equation = ""; 
     equation = equationGenerator(equation, numberOfVariables, variable); 
     System.out.println(equation); 
     System.out.print(calculateAnswer(equation)); 

    } 
    public static String equationGenerator(String equation, int numberOfVariables, Random variable){ 
     int operation; 
     int var; 

     var = variable.nextInt(10)+1; 

     equation += var; 
     operation = variable.nextInt(4)+1; 

     if(numberOfVariables == 1){ 
      equation += " = "; 
      return equation; 
     } 

     if(operation == 1) 
     { 
      equation += " + "; 
     } 
     else if(operation == 2) 
     { 
      equation += " - "; 
     } 
     else if(operation == 3) 
     { 
      equation += "/"; 
     } 
     else if(operation == 4) 
     { 
      equation += " * "; 
     } 

     return equationGenerator(equation, numberOfVariables-1, variable); 
    } 

    public static int calculateAnswer(String equation){ 
     String delims = "[ ]+"; 
     tokens = equation.split(delims); 
     for(i=0; i< tokens.length; i++)      //does all multiplication and division first leaving just addition and subtraction 
      switch(tokens[i]){ 
      case "0": case "1":case "2":case "3":case "4":case "5":case "6":case "7":case "8":case "9": 
       int number = Integer.parseInt(tokens[i]); 
       popOrPush(number); 
       break; 
      case "*": case "/": case "+": case "-": 
       popOrPush(tokens[i], tokens); 
      } 

     while(!numbers.empty()){     //flips number and operation stacks to do addition and subtraction in correct order 
      restOfNumbers.push(numbers.pop()); 
     } 
     while(!operations.empty()){ 
      subAdd.push(operations.pop()); 
     } 
     while(!subAdd.empty()){ 
      switch(subAdd.pop()){ 
      case "+": 
       restOfNumbers.push(restOfNumbers.pop() + restOfNumbers.pop()); 
      case "-": 
       restOfNumbers.push(restOfNumbers.pop() - restOfNumbers.pop()); 
      } 
     } 
     return restOfNumbers.pop(); 
    } 

    public static void popOrPush(int number){ 
     numbers.push(number); 
    } 
    public static void popOrPush(String operation, String[] tokens){ 
     switch(operation){ 
     case "*": 
      int multipliedValue = numbers.pop(); 
      i++; 
      multipliedValue = multipliedValue * Integer.parseInt(tokens[i]); 
      numbers.push(multipliedValue); 
     case "/": 
      int dividedValue = numbers.pop(); 
      i++; 
      dividedValue = dividedValue/Integer.parseInt(tokens[i]); 
      numbers.push(dividedValue); 
     case "+": case "-": 
      operations.push(operation); 
    } 
    } 
}

那么，它是java还是javascript？因为我有消息给你，它不能同时存在。（为什么添加标签时不知道它是什么意思？） –

如果是Java，请查看[this]（http://stackoverflow.com/questions/3422673/evaluating-a-math-expression -given-in-string-form）SO答案。 –

这是Java而不是Javascript。 – sydluce

答

你没有初始化的筹码，所以你要使用numbers变量时可能会得到一个NPE。

确保初始化所有变量（特别是您的堆栈对象）。例如：

Stack<Integer> numbers = new Stack<>();

int形式的字符串方程式答案

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