使用随机整数

Question

Here is the assignment: For this program, there are two "parts". The first part will run the trials and determine how many caps each trial opens before finding a winning cap. Every trial (person) will be a winner. The number of caps opened by each trial is written to the file. The second part of the program will read in the values and calculate the average. The average should be between 4.5 and 5.5 since there is a 1 in 5 chance of winning.

It compiles and runs, but the average is always 0.

My code:

  int randNum = 0; 
  Random randNumList = new Random(); 

  int counter = 0;
  Scanner in = new Scanner(System.in);
  System.out.println("How many trials will there be?");
  int trials = in.nextInt();

  int winner = 0;

  PrintWriter outFile = new PrintWriter (new File("cap.txt")); 
  //run trials
  for (int loop = 1; loop <= trials; loop++)    
  {  
    //select random number until 5 is selected
    randNum = randNumList.nextInt(6);
    for (randNum = randNumList.nextInt(6); randNum == 5; randNum++)
    { 
      randNum = randNumList.nextInt(6);
      counter++;
    }

    outFile.println(loop + " " + randNum);
  }   


  outFile.close ( );    //close the file when finished 

  String token = " ";
  Scanner inFile = new Scanner(new File("cap.txt")); 

  while (inFile.hasNext())
  {      
       token = inFile.next();
       if(token.equals("5"))
         winner++;  
  }

  double average = winner/counter;
  System.out.println("The average number is " + average);

Answer 1

您的cap.txt文件不包含“ 5” =>获胜者= 0，平均值= 0 /计数器= 0（始终）。

Answer 2

winner/counter returns an int not a double (integer division because both operands are integer so the result is truncated). Try this:

winner/(double)counter

That does return a double.

Answer 3

Apart from the int/int division accuracy problem which should be winner/(double)counter or (double)winner/counter try changing your inner for loop to a do while . In general, prefer while when you don't know the exact number of iterations.

Also, randNumList.nextInt(6) is [0-5], thus there are 6 possible outcomes -> there is a 1 in 6 chance of winning . To correct this, use randNumList.nextInt(5) + 1

for (int loop = 1; loop <= trials; loop++) {  
    //select random number until 5 is selected
    do {
        randNum = randNumList.nextInt(5) + 1;
        counter++;
    } while (randNum != 5);

    outFile.println(loop + " " + randNum); //why here?? maybe you should add it below counter++;
}  

also if(token.equals("5")) won't work, as you write (loop + randNum) , it should work if you use outFile.println(randNum);