写一个c语言通讯录管理系统，要求有录入联系人，查询联系人，删除联系人，修改联系人，保存和读取的功能

下面是一个C语言通讯录管理系统的示例代码，包括录入联系人、查询联系人、删除联系人、修改联系人、保存和读取的功能：

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

#define MAX_CONTACTS 1000
#define NAME_LENGTH 20
#define PHONE_LENGTH 20

struct Contact {
    char name[NAME_LENGTH];
    char phone[PHONE_LENGTH];
};

struct Contact contacts[MAX_CONTACTS];
int num_contacts = 0;

void add_contact() {
    if (num_contacts == MAX_CONTACTS) {
        printf("Error: contact list is full\n");
        return;
    }

    struct Contact new_contact;
    printf("Enter name: ");
    scanf("%s", new_contact.name);
    printf("Enter phone number: ");
    scanf("%s", new_contact.phone);

    contacts[num_contacts] = new_contact;
    num_contacts++;

    printf("Contact added successfully\n");
}

void delete_contact() {
    char name[NAME_LENGTH];
    printf("Enter name: ");
    scanf("%s", name);

    int i;
    for (i = 0; i < num_contacts; i++) {
        if (strcmp(contacts[i].name, name) == 0) {
            int j;
            for (j = i; j < num_contacts - 1; j++) {
                contacts[j] = contacts[j + 1];
            }
            num_contacts--;
            printf("Contact deleted successfully\n");
            return;
        }
    }

    printf("Contact not found\n");
}

void list_contacts() {
    int i;
    for (i = 0; i < num_contacts; i++) {
        printf("%s: %s\n", contacts[i].name, contacts[i].phone);
    }
}

void modify_contact() {
    char name[NAME_LENGTH];
    printf("Enter name: ");
    scanf("%s", name);

    int i;
    for (i = 0; i < num_contacts; i++) {
        if (strcmp(contacts[i].name, name) == 0) {
            printf("Enter new phone number: ");
            scanf("%s", contacts[i].phone);
            printf("Contact modified successfully\n");
            return;
        }
    }

    printf("Contact not found\n");
}

void save_contacts() {
    FILE* fp = fopen("contacts.txt", "w");
    if (fp == NULL) {
        printf("Error: could not open file\n");
        return;
    }

    int i;
    for (i = 0; i < num_contacts; i++) {
        fprintf(fp, "%s %s\n", contacts[i].name, contacts[i].phone);
    }

    fclose(fp);

    printf("Contacts saved successfully\n");
}

void load_contacts() {
    FILE* fp = fopen("contacts.txt", "r");
    if (fp == NULL) {
        printf("Error: could not open file\n");
        return;
    }

    num_contacts = 0;

    char name[NAME_LENGTH];
    char phone[PHONE_LENGTH];
    while (fscanf(fp, "%s %s", name, phone) == 2) {
        struct Contact new_contact;
        strcpy(new_contact.name, name);
        strcpy(new_contact.phone, phone);
        contacts[num_contacts] = new_contact;
        num_contacts++;
    }

    fclose(fp);

    printf("Contacts loaded successfully\n");
}

int main() {
    int choice;
    while (1) {
        printf("Enter 1 to add contact, 2 to delete contact, 3 to list contacts, 4 to modify contact, 5 to save contacts, 6 to load contacts, or 7 to quit: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                add_contact();
                break;
            case 2:
                delete_contact();
                break;
            case 3:
                list_contacts();
                break;
            case 4:
                modify_contact();
                break;
            case 5:
                save_contacts();
                break;
            case 6:
                load_contacts();
                break;
            case 7:
                printf("Quitting\n");
                exit(0);
            default:
                printf("Invalid choice\n");
        }
    }

    return 0;
}

该程序使用结构体实现通讯录条目，并使用一个数组来存储所有条目。程序提供了添加、删除、修改、列出、保存和读取通讯录条目的功能，将通讯录保存到名为“contacts.txt”的文件中。