Step 10: Detect Duplicate Contact IDs

Medium Section 2: Add Contact Module

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Problem Statement

Extend the completed Add Contact flow by checking whether the entered contact ID already exists before reading and storing a new record. Keep every earlier ID, name, phone, validation, storage, and counter-update behavior intact. A duplicate ID must print Duplicate ID and stop the current Add operation without creating another record.

Input Format

One or more complete Add Contact operations. Each operation begins with menu choice 1 followed by ID, name, and phone. The sequence ends with menu choice 0.

Output Format

Successful unique contacts print Contact Added. A repeated ID prints Duplicate ID and does not add a second record.

Constraints

IDs must be positive. A contact ID must be unique within the phonebook. The first occurrence of an ID may be stored; subsequent occurrences must be rejected.

Sample Input

Sample Output

Contact Book Ready.
Phonebook Capacity: 100
Contacts: 0
Modules Ready.
Menu:
Add
ID: 101
Valid ID
Name: Alice
Phone: 1234567890
Valid Phone
Contact Added
Menu:
Add
ID: 101
Valid ID
Duplicate ID
Menu:
Exit

Explanation

Duplicate IDs would make ID-based searching, updating, and deleting ambiguous. The phonebook therefore rejects a second record with an existing identifier before accepting its remaining fields.

Starter Code

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

struct Contact {
    int id;
    char name[50];
    char phone[15];
};

struct Contact phonebook[100];
int contact_count = 0;

void add_contact();
void display_contacts();
void search_contact();
void update_contact();
void delete_contact();

void add_contact() {
    int id;

    if (scanf("%d", &id) == 1) {
        printf("\nID: %d", id);

        if (id > 0) {
            printf("\nValid ID");

            // Write your code here

            getchar();

            if (fgets(phonebook[contact_count].name,
                      sizeof(phonebook[contact_count].name), stdin) != NULL) {
                phonebook[contact_count].name[
                    strcspn(phonebook[contact_count].name, "\n")
                ] = '\0';

                printf("\nName: %s", phonebook[contact_count].name);

                {
                    char phone_input[100];

                    if (fgets(phone_input, sizeof(phone_input), stdin) != NULL) {
                        phone_input[
                            strcspn(phone_input, "\n")
                        ] = '\0';

                        printf("\nPhone: %s", phone_input);

                        if (strlen(phone_input) >= 1 &&
                            strlen(phone_input) <= 14) {
                            strcpy(phonebook[contact_count].phone, phone_input);
                            printf("\nValid Phone");

                            phonebook[contact_count].id = id;
                            contact_count++;

                            printf("\nContact Added");
                        } else {
                            printf("\nInvalid Phone");
                        }
                    }
                }
            }
        } else {
            printf("\nInvalid ID");
        }
    }
}

void display_contacts() {
}

void search_contact() {
}

void update_contact() {
}

void delete_contact() {
}

int main() {
    int choice;

    printf("Contact Book Ready.");
    printf("\nPhonebook Capacity: %d", sizeof(phonebook)/sizeof(phonebook[0]));
    printf("\nContacts: %d", contact_count);
    printf("\nModules Ready.");

    while (1) {
        printf("\nMenu:");

        if (scanf("%d", &choice) != 1) {
            break;
        }

        switch (choice) {
            case 1:
                printf("\nAdd");
                add_contact();
                break;

            case 2:
                printf("\nDisplay");
                display_contacts();
                break;

            case 3:
                printf("\nSearch");
                search_contact();
                break;

            case 4:
                printf("\nUpdate");
                update_contact();
                break;

            case 5:
                printf("\nDelete");
                delete_contact();
                break;

            case 0:
                printf("\nExit");
                return 0;

            default:
                printf("\nInvalid Choice");
                break;
        }
    }

    return 0;
}

Limits

Time Limit: 1s
Memory Limit: 256MB

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