Question

在输入有效成绩之前，如何继续提示错误消息？现在，我只提示4次，然后显示平均值。

另外，我如何计算仅有三个最高等级的平均值？

  final int MAX_NUM_GRADES = 4;
      double avg;
      double sum = 0;
      int count = 1;
      double[] examGrade = new double[MAX_NUM_GRADES];
      for (int i = 0; i < examGrade.length; i++) {
         try {
            examGrade[i] = Double.parseDouble(JOptionPane.showInputDialog("Enter Grade " + count + ":"));
            if (examGrade[i] < 0 || examGrade[i] > 100) {
               JOptionPane.showMessageDialog(null,"ERROR!.");           
            }
            else {
               count++;
               sum = sum + examGrade[i];                       
            }
         }
         catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(null,"ERROR!");         
         }      
      }
      avg = sum/examGrade.length;
      JOptionPane.showMessageDialog(null,"average exam grade is: " 
         + String.format("%.1f",avg));

Answer 1

这是因为您的for循环仅通过examGrade数组的长度进行迭代，该数组在程序开始时使用MAX_NUM_GRADES设置为4。

相反，您可以尝试跟踪有效答案，只计算一次使用while-loop回答3个有效成绩。下面使用的TreeSet会自动对输入到集合中的值进行排序，因此会为您完成排序。

像这样：

TreeSet<Double> grades = new TreeSet<Double>();
final int MAX_NUM_GRADES = 4;
double avg;
double sum = 0;
double temp = 0d;

while(grades.size() < MAX_NUM_GRADES){
     temp = Double.parseDouble(JOptionPane.showInputDialog("Enter Grade " + count + ":"));
     if (examGrade[i] < 0 || examGrade[i] > 100) {
         JOptionPane.showMessageDialog(null,"ERROR!.");           
     } else {
         grades.add(temp);                   
     }
}
for (Double val : grades) {
    sum += val;
}
avg = sum/grades.size();
  JOptionPane.showMessageDialog(null,"average exam grade is: " 
     + String.format("%.1f",avg));

只需将try-catch块添加到您想要的位置即可。

Answer 2

我建议把它放在循环中。下面是一个psudo代码示例。

for(int I = 0; I < examGrade.length; I++) {
    invalid = true;
     while(invalid) {
        //Accept the input, set invalid = false if it is correct
    }
}

Answer 3

你需要一个while或一个do while循环，你一直循环直到输入有效

final int MAX_NUM_GRADES = 4;
  double avg;
  double sum = 0;
  int count = 1;
  double[] examGrade = new double[MAX_NUM_GRADES];
  boolean valid; // this is true when the input is valid
  for (int i = 0; i < examGrade.length; i++) {
     valid=false;// initialize valid
     try {
        do{
        examGrade[i] = Double.parseDouble(JOptionPane.showInputDialog("Enter Grade " + count + ":"));
        if (examGrade[i] < 0 || examGrade[i] > 100) {
           JOptionPane.showMessageDialog(null,"ERROR!.");
           valid=false;//in this case input is not valid           
        }
        else {
           count++;
           sum = sum + examGrade[i];
           valid=true;// input is valid                       
        }
       }while(!valid)//keep looping while valid is false
     }
     catch (NumberFormatException e) {
        JOptionPane.showMessageDialog(null,"ERROR!");         
     }      
  }
  avg = sum/examGrade.length;
  JOptionPane.showMessageDialog(null,"average exam grade is: " 
     + String.format("%.1f",avg));

现在计算你需要对数组进行排序的3个最高等级的平均值，然后选择最后3个等级，你可以使用任何排序算法，例如：

int tmp;
for(int i=0;i<examGrade.length;i++){
  for(int j=i;j<examGrade.length;j++{
  if(examGrade[j]<examGrade[i]){
    tmp=examGrade[j];
    examGrade[j]=examGrade[i];
    examGrade[i]=tmp;
   }
  }
  //now that its sorted you can calculate the average of highest scores
   float avg=0;
   for(int i=1;i<examGrade.length;i++){
     avg+=examGrade[i];
    }
   avg=avg/3;

Answer 4

将您的代码更改为：

  final int MAX_NUM_GRADES = 4;
  double avg;
  double sum = 0;
  double min = Double.MAX_VALUE;
  int count = 1;
  double[] examGrade = new double[MAX_NUM_GRADES];
  for (int i = 0; i < examGrade.length; i++) {
     boolean invalid = true;
     while(invalid) {
     try {
        examGrade[i] = Double.parseDouble(JOptionPane.showInputDialog("Enter Grade " + count + ":"));
        if (examGrade[i] < 0 || examGrade[i] > 100) {
           JOptionPane.showMessageDialog(null,"ERROR!.");           
        }
        else {
           invalid = false;
           count++;
           sum = sum + examGrade[i];
           if(examGrade[i] < min) min = examGrade[i]; 
        }
     }
     catch (NumberFormatException e) {
        JOptionPane.showMessageDialog(null,"ERROR!");         
     }
     }      
  }
  avg = (sum - min)/(examGrade.length - 1);
  JOptionPane.showMessageDialog(null,"average exam grade is: " 
     + String.format("%.1f",avg));

如何在数组中不断提示错误消息

4 个答案: