Question

我的问题是关于增量我问你如何从do while循环返回数据，假设要在每个值中设置。

我的do while循环中的totalSales在循环出来时应该有数据集，它不会将数据保存到totalSales或totalItems值中。

// The system print out values are empty.
      System.out.printf(salesID + " you entered a total of: " + totalItems + "With a total sales of $%15.2f" + totalSales);

我试图从一个怪异的do或if语句循环返回数据，它不会返回我设置的项目为什么？

// yesno to n for first loop through.

do {
      System.out.println("Welcome Sales ID: " + salesID + " please enter the samsung TV sold: \n");
      samsungProduct = scanValue.next();
      System.out.println("Please enter your total TV sales amounts individually for today \n");
      singleSale = scanValue.nextDouble();
      totalSales = totalSales + singleSale;
      totalItems = totalItems++;
      System.out.println("Do you want to enter another sales total(Y/N): \n ");
      yesNo = scanValue.next();

}        while (!yesNo.equalsIgnoreCase("N"));

// get the items set inside of the do while loop.

// The system print out values are empty.
      System.out.printf(salesID + " you entered a total of: " + totalItems + "With a total sales         of  $%15.2f" + totalSales);

Answer 1

这是错误的：

totalItems = totalItems++;

你应该做

totalItems++;

你所做的就等于：

int temp = totalItems;
totalItems = totalItems + 1;// (totalItems++)
totalItems = temp;

Answer 2

这是您的问题：totalItems = totalItems++;

在这行代码之后，totalItems的值不会改变。

使用totalItems++;代替

问题是i ++递增i，但返回旧值。所以，当你执行i = i++时，你将旧值分配给i - 所以我没有改变。

Answer 3

totalItems = totalItems++;是无操作的。

请参阅此处：Post Increment Operator And Assignment

System.out.printf(salesID + " you entered a total of: " + totalItems 
    + "With a total sales of $%15.2f" + totalSales);

应该是

System.out.printf(salesID + " you entered a total of: " + totalItems 
       + "With a total sales of $%15.2f", totalSales);
                                       ^^^^

Answer 4

我没有看到你的循环出现任何明显错误，但是运行它（创建了适当的变量）导致了这个异常：

Exception in thread "main" java.util.MissingFormatArgumentException: Format specifier '15.2f'
    at java.util.Formatter.format(Formatter.java:2432)
    at java.io.PrintStream.format(PrintStream.java:920)
    at java.io.PrintStream.printf(PrintStream.java:821)
    at ScratchMain.main(ScratchMain.java:26)

这告诉我你没有正确使用printf。如果您使用$f（或更复杂的$%15.2f），那么您要放在那里的值需要作为参数传递给printf而不是刚刚连接到String：

System.out.printf(salesID + " you entered a total of: " + totalItems + "With a total sales         of  $%15.2f", totalSales);

此外，你有代码totalItems = totalItems++;，这实际上是一个无操作（即它什么都不做）。将其替换为 <{em> totalItems++;或totalItems = totalItems + 1;（如果您想明确说明）。

Java虽然看起来正确编码返回值？

4 个答案: