需要帮助在 for 循环中声明变量（Java）

Question

我目前正在编写一个程序，但在尝试执行 for 循环时遇到了错误。我想在for循环中声明一个变量，然后一旦该变量获得某个值就中断，但是它返回错误“无法解析为变量”。

这是我的代码

int i = -1;
for (; i == -1; i = index)     
{ 
    Scanner scan = new Scanner(System.in);
    System.out.println("Please enter your first and last name");
    String name = scan.nextLine();
    System.out.println("Please enter the cost of your car,"
                     + "\nthe down payment, annual interest rate,"
                     + "\nand the number of years the car is being"
                     + "\nfinanced, in that order.");
    DecimalFormat usd = new DecimalFormat("'$'0.00");
    double cost = scan.nextDouble();
    double rate = scan.nextDouble();
    int years = scan.nextInt();
    System.out.println(name + ","
                   +  "\nyour car costs " + usd.format(cost) + ","
                   +  "\nwith an interest rate of " + usd.format(rate) + ","
                   +  "\nand will be financed annually for " + years + " years."
                   +  "\nIs this correct?");
    String input = scan.nextLine();
    int index = (input.indexOf('y'));
}

我想运行程序的输出段，直到用户输入是，然后循环中断。

Answer 1

在这里你想使用一个while循环。通常你可以通过大声说出你的逻辑来决定使用哪个循环，而这个变量是（不是）（值）这样做。

对于你的问题，在循环外初始化变量，然后在里面设置值。

String userInput = null;
while(!userInput.equals("exit"){
  System.out.println("Type exit to quit");
  userInput = scan.nextLine();
} 

Answer 2

你不能这样做。如果变量是在循环内声明的，那么每次运行都会重新创建它。为了成为退出循环的条件的一部分，它必须在它之外声明。

或者，您可以使用break 键来结束循环：

// Should we exit?
if(input.indexOf('y') != -1)
    break;

Answer 3

您可以使用 do-while 代替 for 循环（它更适合这种情况。

boolean exitLoop= true;
do
{
    //your code here
    exitLoop=  input.equalsIgnoreCase("y");
} while(exitLoop);

Answer 4

对于无限循环，我更喜欢while。

boolean isYes = false;
while (!isYes){ 
Scanner scan = new Scanner(System.in);
System.out.println("Please enter your first and last name");
String name = scan.nextLine();
System.out.println("Please enter the cost of your car,"
                     + "\nthe down payment, annual interest rate,"
                     + "\nand the number of years the car is being"
                     + "\nfinanced, in that order.");
DecimalFormat usd = new DecimalFormat("'$'0.00");
double cost = scan.nextDouble();
double rate = scan.nextDouble();
int years = scan.nextInt();
System.out.println(name + ","
                   +  "\nyour car costs " + usd.format(cost) + ","
                   +  "\nwith an interest rate of " + usd.format(rate) + ","
                   +  "\nand will be financed annually for " + years + " years."
                   +  "\nIs this correct?");
String input = scan.nextLine();
isYes = input.equalsIgnoreCase("yes");
}

Answer 5

变量index的作用域是for循环块的局部变量，而不是for循环本身，所以你不能在for循环中说i = index。

反正你不需要index。这样做：

for (; i == -1;)

甚至

while (i == -1)

最后……

    i = (input.indexOf('y'));
}

顺便说一句，我不确定你想要input.indexOf('y')； "blatherskyte" 的输入将触发此逻辑，而不仅仅是 "yes"，因为输入中有 y。