在数组C 中排序最大和最小的值

Question

这是一个非常简单且常见的练习，尽管我遇到了一个错误，但我似乎无法理解，并且在任何地方都找不到解释，因为它可能太具体了。

该程序只是提示用户输入第1到10人吃多少煎饼，然后打印出某人吃的煎饼数量最大的是什么。我的问题是，"手工循环"整理出最大和最小的值有效，但是该算法（在本论坛上强烈建议使用而不是手工循环）不会打印出正确的>最大的值，但适用于最小的。

这是我的代码：

void pancakes() {
    int pan[11];
    int small, big;
    for (int i = 1; i < 11; i++)  // counts to 11-1 and prompts user for pancakes
                                  // eaten by person 1==>10
    {
        cout << "How many pancakes did person " << i << " eat?n";
        cin >> pan[i];
    }
    big = small = pan[1];  // assigns element to be highest or lowest value
    for (int i = 1; i < 11; i++) {
        if (pan[i] > big)  // compare biggest value with current "big" element
        {
            big = pan[i];
        }
        if (pan[i] < small)  // compares smallest value with current "small" element
        {
            small = pan[i];
        }
    }
    cout << "The person who ate the most pancakes ate " << big << " of them."
             << endl;  // prints biggest value
    cout << "The person who ate the least pancakes ate " << small << " of them."
             << endl;  // prints smallest value
    auto minmax = minmax_element(begin(pan), end(pan));
    cout << "min element " << *(minmax.first) << "n";
    cout << "max element " << *(minmax.second) << "n";
}   

，这是控制台返回的内容：

How many pancakes did person 1 eat?
45
How many pancakes did person 2 eat?
64
How many pancakes did person 3 eat?
7
How many pancakes did person 4 eat?
34
How many pancakes did person 5 eat?
87
How many pancakes did person 6 eat?
45
How many pancakes did person 7 eat?
89
How many pancakes did person 8 eat?
32
How many pancakes did person 9 eat?
55
How many pancakes did person 10 eat?
66
The person who ate the most pancakes ate 89 of them.
The person who ate the least pancakes ate 7 of them.
min element 7
max element 1606416304

Answer 1

auto minmax = minmax_element(begin(pan), end(pan));

确实找到了最小/最大值，但是C 中的数组索引从0开始。您从1个索引开始填充int pan[11];，

big=small=pan[1]; //assigns element to be highest or lowest value; change to pan[0]
for (int i = 1; i < 11; i++){...} // change to i=0

因此，pan[0]将包含垃圾，在您的情况下（值1606416304）将由minmax_element考虑。

实际上，从非命令变量读取是C和C 中的不确定行为，尽管大多数情况下，您都会读取在该内存地址中存储的内容。

如果您使用C 11（现在您应该使用），那么您也可以使用基于范围的循环处理煎饼：）

for(auto& pancake: pan) // note the reference, we are reading
{
    cin >> pancake; // to read
}

和

for(auto pancake: pan)
{
    // further processing here, like
    if(pancake < small) { small = pancake;} // etc
}

Answer 2

您的数组是11号的数组，但是您只循环超过10个元素，而第一个元素则是非初始化的。这意味着它包含垃圾（未定义的行为），在这种情况下，1606416304，最大，不是吗？=）

从：

更改循环

for (int i = 1; i < 11; i++)

to：

for (int i = 0; i < 11; i++)

std :: minmaxelement（）然后随心所欲。

---

后果：

通常，在处理与预期结果不同的功能时，一个常见的错误是检查您的数据您提供该功能。这样，您知道数据是否有问题或/和功能。在您的情况下，打印阵列会让您了解数据不好！

Answer 3

您的pan数组定义为具有11元素，但您仅初始化其中10个。值得注意的是，pan[0]永远不会初始化，并且会有一些随机值。我猜您的随机价值恰好是1606416304。