我试图通过编写一个程序来学习C语言的基础知识，该程序提示用户输入整数，然后将这些值存储在一个链表中。如果输入值为-128或更小，则current节点被设置为NULL，提示符结束。然后，该程序遍历链表并计算输入值的平均值。然而，列表的计数器总是比预期多一个元素，从而导致不正确的平均值，尽管我在添加每个值和递增计数器之前显式指定了NULL检查。
代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

int main()
{
    struct record {
        int temperature;
        struct record *next;
    };
    
    // Keep hold of the first record for iterating --v
    struct record *first = NULL;
    first = (struct record *)malloc(sizeof(struct record));
    
    // Keep hold of the current record used in the while loop --v
    struct record *current = first;
    
    while (true) {
        
        // Get user input --v
        int temp;
        printf("Enter measurement: ");
        scanf("%d", &temp);
        
        // If input is less than -128, end the loop --v
        if (temp <= -128) {
            current = NULL;
            break;
        }
        
        // Record the temperature --v
        current->temperature = temp;
        
        // Allocate memory for the next record --v
        current->next = (struct record *)malloc(sizeof(struct record));
        
        // The next now becomes the current because we are done with the current --v
        current = current->next;
        printf("Next record created!\n");
    }
    
    // Calculate average --v
    current = first;
    double sum = 0.;
    int count = 0;
    // As long as the record is not NULL --v
    while (current != NULL) {
        
        sum += current->temperature;
        count++;
        
        printf("%d %d\n", count, current->temperature);
        
        // Move to the next record --v
        current = current->next;
    }
    
    printf("\nAverage of the list values: %.1f", sum / count);
}

这是正确的行为吗？C中是否有一些我不知道的机制？
我添加了一些调试行，以便跟踪计数器以及相应的记录，并发现current属性看起来并不为NULL，尽管我显式地将其设置为NULL。

Enter measurement: 22
Next record created!
Enter measurement: 22
Next record created!
Enter measurement: 22
Next record created!
Enter measurement: -128
1 22
2 22
3 22
4 0

Average of the list values: 16.5

我确实尝试过使用free(current)来释放current指针的内存，但结果并不好，因为temperature只保存了一个随机数。