问题

警告：我对编程极为陌生。如果这段代码看起来很混乱，那是因为确实如此。

我曾经把这段代码完美地运行起来……直到我的笔记本突然重启，我失去了所有的代码。我不得不重新写，但现在，出于某种原因，当我输入一个数组时，它会多加一个数字。

```c
#include <stdio.h>

int main()
{
    int length = 0;
    int arr[length];
    int i;
    
    do {
        printf("请输入一个正整数：\n");
        scanf("%d", &length);
        if (length <= 0)
            printf("长度无效，请重试。\n");
    }
    while (length <= 0);
    
    printf("请输入%d个数字：\n", length);
    do {
        for (int i = 0; i <= length; ++i) {
            scanf("%d", &arr[i]);
        }
    } 
    while (length <= 0);
    
    int min = arr[0];
    int max = arr[0];
    double sum = arr[0];
    
    for (int i = 1; i <= length; i++) {
        if (arr[i] > max) {
            max = arr[i];
        }
        if (arr[i] < min) {
            min = arr[i];
        }
        sum = sum + arr[i];
    }
  
    printf("最小值为：%d\n 最大值为：%d\n 平均值为：%f\n", min, max, sum/length);
    return 0;
}

示例：数组长度 = 5，数组 = 1 2 3 4 5
最小值 = 1，最大值 = 6，平均值 = 4

我感到困惑和沮丧。我无法再看这个了。

<details>
<summary>英文:</summary>

**Warning: I am extremely new to coding. If this code looks like a mess, it&#39;s because it is.**

I had this code literally working perfectly... until my laptop restarted randomly and I lost all my code. I had to rewrite it and now, for some reason, when I enter an array, it adds one extra number to it. 

#include <stdio.h>

int main()
{
int length = 0;
int arr[length];
int i;

do {
    printf("please enter a positive nonzero integer: \n");
    scanf("%d", &length);
    if (length <= 0)
    printf("Length is invalid. Try again. \n");
}
while (length <= 0);

printf("please enter %d numbers: \n", length);
do {
    for (int i = 0; i <= length; ++i) {
      scanf("%d", &arr[i]);
    }
    } 
    while (length <= 0);
    
int min = arr[0];
int max = arr[0];
double sum = arr[0];

for (int i = 1; i <= length; i++) {
    if (arr[i] > max) {
        max = arr[i];
    }
    if (arr[i] < min) {
        min = arr[i];
    }
    sum = sum + arr[i];

}

printf("Minimum is: %d\n Maximum is: %d\n Mean is: %f\n", min, max, sum/length);
return 0;
}

Example: array length = 5, array = 1 2 3 4 5
min= 1, max = 6, mean = 4

I'm so stuck and just defeated. I can't look at this any more.

</details>


# 答案1
**得分**: 2

在C语言中，数组的索引从`0`开始。长度为`5`的数组的索引分别为`0`、`1`、`2`、`3`和`4`。通过检查你的索引是否小于或等于长度，你正在进行越界访问。这会导致未定义的行为。

举例来说，你的`for`循环应该如下所示，将`&lt;=`替换为`&lt;`，并从`0`开始：

```c
for (int i = 0; i < length; i++) {
    if (arr[i] > max) {
        max = arr[i];
    }

    if (arr[i] < min) {
        min = arr[i];
    }

    sum = sum + arr[i];
}

for (int i = 0; i < length; i++) {
    if (arr[i] > max) {
        max = arr[i];
    }

    if (arr[i] < min) {
        min = arr[i];
    }

    sum = sum + arr[i];
}