这个程序还没有完全准备好，所以不是所有的功能都编好了。
但是，当涉及到非常基本的功能时，我面临着一个问题：将所述节点添加到所述链表的末尾。
不知何故，我在链表的开头得到了一个神秘的数字"0"，但我不知道它来自哪里

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>

typedef struct USER{
    int number;
    struct USER *next;
}USER;

USER* allocMem(USER* newUser){
    if ((newUser = (USER*)malloc(sizeof(USER))) == NULL ){
        perror("Memory allocation failed.");
        exit(1);
    }
    newUser->number;
    printf("A list has been created.\n");
    return newUser;
}

int newNode(USER* start){
    int num;
    USER *newUser = NULL; 
    USER *value = NULL;
    if ((newUser = (USER*)malloc(sizeof(USER))) == NULL ){
        perror("Memory allocation failed.");
        exit(1);
    }
    printf("\nGive a new number: ");
    scanf("%d", &num);
    newUser->number = num;
    newUser->next = NULL;
    if (start == NULL){
        start = newUser;
    }else{
        value = start;
        while(value->next != NULL){
            value = value->next;
        }
        value->next = newUser;
    }
    return 0;
}

int newNode_position(USER* start){
    USER *newUser = NULL;
    USER *value = NULL;
    int num;
    int position;
    if ((newUser = (USER*)malloc(sizeof(USER))) == NULL ){
        perror("Memory allocation failed.");
        exit(1);
    }
    printf("\nGive a new number: ");

    scanf("%d", &newUser->number);

    printf("Into which node do you want to place the number: ");
    scanf("%d", &position);
    value = start;
    for(int i = 1; i < position; i++){  
        value = value->next;
        
    }
    newUser->next = value->next; 
    value->next = newUser;

    value = NULL;
    value = start;
    printf("The following numbers are in the list: \n");
    while(value->next != NULL){
        printf("%d ", value->number);
        value = value->next;
    }

    return 0;
}

void print(USER *start){
    USER *value = NULL;
    value = start;
    printf("Following numbers are now in the list: \n");
    while(value->next != NULL){
        printf("%d ", value->number);
        value = value->next;
    }
    printf("\n");
}

void freeMem(USER* start){ 
    USER *value = NULL;
    while (start != NULL){
        value = start;   
        start = value->next;
        free(value); 
    }
}


int main(void){
    int choice;
    USER *start = NULL;
    printf("This program let's you create a linked list and manage it.\n");
    do {
        printf("\n1) Create a list\n");
        printf("2) Insert a new node in the end\n");
        printf("3) Insert a new node in the middle, to a specified position\n");
        printf("4) Clear the list\n");
        printf("5) Delete certain node from the list\n");
        printf("6) Print the list\n");
        printf("0) Quit\n");
        printf("Your choice: ");
        scanf("%d", &choice);
        switch(choice){
            case 1:
            start = allocMem(start);  
            break;
            case 2:
            newNode(start);
            break;
            case 3:
            newNode_position(start);
            case 4:
            freeMem(start);
            break;
            case 6:
            print(start);
            break;
            case 0:
            printf("\nThank you for using the program.");
            break;
            default:
            printf("Unknown choice.");
            break;
        }
    } while(choice != 0);
    
}

• • 输出：**
• • 创建列表并添加编号时："2"在列表末尾三次，输出为：**

0、2、2

• • 当它应该**

二、二、二
我不明白为什么它在开头打印神秘的0。