Use a pointer to address elements in an array

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

# # define MAX 50

typedef struct contact_st
{
    char Name[10];
    char PhoneNumber[13];
} } Contact;

Contact PhoneBook[MAX];




int contactSwap(void* arr, int i, int j)
{
    int temp;
    temp = ((int*)arr + i);
    *((int*)arr + i) = ((int*)arr + j);
    *((int*)arr + j) = temp;

    // // Goal: arr[i] <- arr[j], arr[j] <- arr[i]
    // // calculate address for arr[i]:  ((int*)arr+i)
    // // derefernce int: *((int*)arr+i))
}

int main() {
    Contact A[5] = { { "Roki", "12345678" }, { "Thor", "33333333" }, { "IronMan","3765898" }, { "Hulk", "74561253" }, { "Groot", "99999999" } };

    for (int i = 0; i < 4; i++)
    {
        for (int j = 0; j < 4 - i; j++)
        {
            if (*((Contact*)A + i)->PhoneNumber, *((Contact*)A + j)->PhoneNumber){
            contactSwap(A, i, j);
            }
        }
    }

    void *vp;
    vp = A;
    for (int i = 0; i < 5; i++)
    {
        // // Calculate address for arr[i]:  ((Contact*)arr+i)
        // // derefernce structure Contact: *((Contact*)arr+i)).Name
        // // for stucture we use ->: ((Contact*)vp+i)->Name
        printf("Addr vp:%p\t", (Contact*)vp + i);
        printf("name:%s\t phone:%s\n", ((Contact*)vp + i)->Name, ((Contact*)vp + i)->PhoneNumber);
    }
    printf("\n");

}