在c语言中用单链表实现通讯录系统，具有输入，查找，添加，删除，修改和输出功能

在C语言中，我们可以使用结构体和指针来构建一个简单的单链表通讯录系统。首先，我们需要定义一个包含姓名和联系方式的节点结构：

typedef struct Contact {
    char name[50];
    char phone[20];
    struct Contact* next;
} Contact;

接下来，我们创建一些基本操作的函数：

1. **输入**：允许用户输入新联系人信息

void addContact(Contact** head, char* name, char* phone) {
    Contact* newNode = (Contact*)malloc(sizeof(Contact));
    strcpy(newNode->name, name);
    strcpy(newNode->phone, phone);
    newNode->next = NULL;

    if (*head == NULL) {
        *head = newNode;
    } else {
        Contact* current = *head;
        while (current->next != NULL) {
            current = current->next;
        }
        current->next = newNode;
    }
}

2. **查找**：按名字查找特定联系人

Contact* searchByName(Contact* head, char* name) {
    Contact* current = head;
    while (current != NULL && strcmp(current->name, name) != 0) {
        current = current->next;
    }
    return current;
}

3. **删除**：按名字删除联系人

void deleteContact(Contact** head, char* name) {
    if (*head == NULL || (*head)->name == NULL) return;
    
    Contact* temp = *head;
    Contact* prev = NULL;
    
    if(strcmp(temp->name, name) == 0){
        *head = temp->next;
        free(temp);
        return;
    }

    while(temp != NULL && strcmp(temp->name, name) != 0){
        prev = temp;
        temp = temp->next;
    }
    
    if(temp != NULL){
        prev->next = temp->next;
        free(temp);
    }
}

4. **修改**：更新联系人的信息

void updateContact(Contact** head, char* oldName, char* newName, char* newPhone) {
    Contact* contact = searchByName(head, oldName);
    if (contact != NULL) {
        strcpy(contact->name, newName);
        strcpy(contact->phone, newPhone);
    }
}

5. **输出**：遍历链表显示所有联系人

void displayContacts(Contact* head) {
    if (head == NULL) {
        printf("通讯录为空\n");
    } else {
        Contact* current = head;
        while (current != NULL) {
            printf("姓名：%s，电话：%s\n", current->name, current->phone);
            current = current->next;
        }
    }
}