没有条件值的 FOR 循环 "for (int i = 1; ; i++)" 不能正常工作

Question

我发现了一个帖子，其中使用了 FOR 循环而没有 CONDITION 值。这是一个循环：

for (INITIALIZATION; CONDITION; AFTERTHOUGHT) 
{
    // Code for the for-loop's body goes here.
}

跳过 CONDITION 值是不安全的，但如果你使用if/else 语句，它可以做到。请看一下我的 for 循环：for (int i = 1; ; i++) 和里面的实现。出于某种原因，if/else 语句我没有得到正确的逻辑。

#include <iostream>
using namespace std;

int main() {

    int boxes;
    int boxes_for_sale;

    cout << "Enter quantity of the boxes in warehouse: > " << flush;
    cin >> boxes;
    cout << "Enter quantity of the boxes for sale: > " << flush;
    cin >> boxes_for_sale;

    for (int i = 1;; i++) {

        if (boxes < boxes_for_sale) {
            cout << "There are not enough boxes in warehouse!" << endl;
            cout << "Enter quantity of the boxes for sale: > " << flush;
            cin >> boxes_for_sale;
        }
        else
            boxes -= boxes_for_sale;
            cout << "Car N:" << i << " is full\n" << "You have " << boxes << "boxes for sale" << endl;

        if (boxes == 0)
            cout << "Sold out!" << endl;
            break;

    }
    return 0;
}

Answer 1

由于您没有指定程序所需的行为，我将仅说明代码中发生的情况。

可能会做一些意想不到的代码的重要sn-ps：

 for (int i = 1;; i++) 

这是完全合法的，但请注意没有指定终止条件。除非您 break 退出，否则您将陷入无限循环。

else
    boxes -= boxes_for_sale;
    cout << "Car N:" << i << " is full\n" <<
    "You have " << boxes << "boxes for sale" << endl;

我可以根据缩进猜测，您希望两行仅在 else 之前的 if 语句为假时执行，但这不是正在发生的事情。

由于您没有使用花括号指定 else 块，因此只有 else 之后的第一条语句会在您需要时执行。 cout 将始终执行。

你有同样的问题：

if (boxes == 0)
        cout << "Sold out!" << endl; //will output only if boxes==0
        break; //will break out of loop in any case

Answer 2

#include <iostream>
using namespace std;

int main() {

    int boxes;
    int boxes_for_sale;

    cout << "Enter quantity of the boxes in warehouse: > " << flush;
    cin >> boxes;
    cout << "Enter quantity of the boxes for sale: > " << flush;
    cin >> boxes_for_sale;

    for (int i = 1;; i++) {

        if (boxes < boxes_for_sale) {
            cout << "There are not enough boxes in warehouse!" << endl;
            cout << "Enter quantity of the boxes for sale: > " << flush;
            cin >> boxes_for_sale;
        }
        else{
            boxes -= boxes_for_sale;
}
            cout << "Car N:" << i << " is full\n" << "You have " << boxes << "boxes for sale" << endl;

        if (boxes == 0)
 {           cout << "Sold out!" << endl;
            break;}

    }
    return 0;
}

Answer 3

注意大括号，你需要为每个for循环，if语句和else语句放置大括号。

还要注意缩进，以实现良好的编程习惯。

#include <iostream>
using namespace std;

int main() 
{

    int boxes;
    int boxes_for_sale;

    cout << "Enter quantity of the boxes in warehouse: > " << flush;
    cin >> boxes;
    cout << "Enter quantity of the boxes for sale: > " << flush;
    cin >> boxes_for_sale;

    for (int i = 1;; i++) {

        if (boxes < boxes_for_sale) 
        {
            cout << "There are not enough boxes in warehouse!" << endl;
            cout << "Enter quantity of the boxes for sale: > " << flush;
            cin >> boxes_for_sale;
        }
        else
        {
            boxes -= boxes_for_sale;
            cout << "Car N:" << i << " is full\n" << "You have " << boxes <<       boxes for sale" << endl;
        }
        if (boxes == 0)
       {
            cout << "Sold out!" << endl;
            break;
       }

    }
    return 0;
}

Answer 4

对不起，伙计们缺乏描述。这是我在这里的第一个问题，下次我会更具体。

这是我尝试做的。

int main() {

    int boxes_in_warehouse;
    int boxes_for_sale;
    cout << "Enter quantity of the boxes in warehouse: " << flush;
    cin >> boxes_in_warehouse;
    cout << "Enter quantity of the boxes for sale: " << flush;
    cin >> boxes_for_sale;

    if (boxes_in_warehouse < boxes_for_sale) {
        cout << "No, Enter quantity of the boxes for sale: " << flush;
        cin >> boxes_for_sale;
    }

    boxes_in_warehouse -= boxes_for_sale;

    while (boxes_in_warehouse > 0) {
        cout << "You have " << boxes_in_warehouse << " left" << endl;
        cout << "Please enter quantity of the boxes for sale again" << endl;
        cin >> boxes_for_sale;
        boxes_in_warehouse -= boxes_for_sale;
    }

    cout << "we are sold out" << endl;
    return 0;
}

应该运行到 box_in_warehouse == 0 的代码意味着售罄。

如果你能优化我最后的代码，我会很高兴看到你的版本。