创建结构并传递功能

Question

I need a help with proper creating function and then passint it to function. I had a piece of code like this:

struct phones {
    char lastname[15];
    char number[8];
    char city[15];
} *list;

void enter(phones[], int);
int main()
{
    int n;
    cout << "Enter the number of users: ";
    cin >> n;
    list = new phones[n];
    enter(list, n);
    system("pause");
    delete[]list;
    return 0;
}
void enter(phones list[], int n) {
    for (int i = 0; i < n; i++)
    {
        cout << "User number " << i + 1 << endl;
        cout << "Enter user's lastname ";
        cin >> list[i].lastname;
        cout << "Enter user's number: ";
        cin >> list[i].number;
        cout << "Enter user's city: ";
        cin >> list[i].city;
    }
}

My teacher told me that it's not good to create a structure using *list right in it. Now i have a question how to create the structure properly, declare a size from user's input and then pass it to function.

Answer 1

You can always define variables after declaring a struct :

phones *list;

C++ doesn't have VLA so either use dynamic allocation, which is disallowsled according to your description, or use the special stuff in C++: STL.

Create a vector of struct phones can make it very simple:

#include <vector>

// After input number
std::vector<phones> list(n);

And you won't have to bother with new s and delete s.

Answer 2

Just for fun, I rewrote your program, including a function to display the read data. This is how I would have it:

#include <cstdlib>
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

struct User {
  char lastname[15];
  char number[8];
  char city[15];
};

void enter(User users[], int n)
{
  for (int i = 0; i < n; ++i) {
    cout << "[User number " << (i + 1) << "]" << endl;
    cout << "Enter user's lastname: ";
    cin >> users[i].lastname;
    cout << "Enter user's number: ";
    cin >> users[i].number;
    cout << "Enter user's city: ";
    cin >> users[i].city;
  }
}

void show(User users[], int n)
{
  for (int i = 0; i < n; ++i) {
    cout << "[User number " << (i + 1) << "]" << endl;
    cout << "Lastname: " << users[i].lastname << endl;
    cout << "Number: " << users[i].number << endl;
    cout << "City: " << users[i].city << endl;
  }
}

int main()
{
  int n;
  cout << "Enter the number of users: ";
  cin >> n;
  User* users = new User[n];
  enter(users, n);

  cout << "-- Displaying users: --" << endl;
  show(users, n);

  system("pause");
  delete[] users;
  return 0;
}

Answer 3

You could also eliminate the problem in your program by preceding a typedef before struct and using the List

example as follow:

typedef struct Person {
  char lastname[15];
  char number[8];
  char city[15];
} * List;

void enter(List list, int n) ;
void show(List list, int n);
int main()
{
  int n;
  cout << "Enter the number of users: ";
  cin >> n;
  List users = new Person[n];
  enter(users, n);
  cout << "-- Displaying users: --" << endl;
  show(users, n);
  system("pause");
  delete[] users;
  return 0;
}

void show(List list, int n)
{
  for (int i = 0; i < n; ++i) {
    cout << "[User number " << (i + 1) << "]" << endl;
    cout << "Lastname: " << list[i].lastname << endl;
    cout << "Number: " << list[i].number << endl;
    cout << "City: " << list[i].city << endl;
  }

}

void enter(List list, int n) {
    for (int i = 0; i < n; i++)
    {
        cout << "User number " << i + 1 << endl;
        cout << "Enter user's lastname ";
        cin >> list[i].lastname;
        cout << "Enter user's number: ";
        cin >> list[i].number;
        cout << "Enter user's city: ";
        cin >> list[i].city;
    }
}