#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string.h>
using namespace std;

//Two global variables for the "fixed" administrator name and password to be easily changed.
char adminname[] = "admin";
char adminpass[] = "pass";

class userscloud;

//Every object of the class User is one user of the network.
class User {

    char name[31],loginname[31],password[31];
    int id,friends[10],friendsnum;

    public:
        char const* getname() const {return name;};
        char const* getloginname() const {return loginname;};
        char const* getpassword() const {return password;};
        int getid() const {return id;};
        void addfriend(int totusers);
        void delfriend();
        void printfriends() const;
        User(int ids);//Constructor for User-type objects.
};

//A class that contains an array of pointers to each User object.
class userscloud{
    User *usersarray;
	public:
	    userscloud(int num);//Constructor for the userscloud object.
	    User getuser(int temp) const;
};

User userscloud::getuser(int temp) const{
    return usersarray[temp];
}

userscloud::userscloud(int num){

    if (num==1){ //If it's the first time here, allocate enough memory.
        if ( (usersarray=(User *)malloc (sizeof(User))) == NULL){
            cout<<"Not enough memory! \n";
            exit(1);
        }
    }
    else{ //Expand allocated memory.
        if ( (usersarray = (User *) realloc(usersarray,num*sizeof(User))) == NULL){
            cout<<"Not enough memory! \n";
            exit(2);
        }
    }
    usersarray[num-1]=User(num);
}

User::User(int ids){ //User class constructor gets user's name, password and login name as inputs.
    cout << "Give name, login name and password for the new user ( <=30 characters eatch ) \n";
    cin >> name >> loginname >> password;
    id=ids;
    friendsnum=0;
    for (int l=0;l<9;l++){
        friends[l]=0;
    }
}

int loginpross(userscloud Obj,int totusers){ //Gets a login name as input, finds if this login name exists, if yes then also checks the password.
    char temploginname[31], temppassword[31];

    cout << "Give your login name. \n";
    cin >> temploginname;

    if (!strcmp(temploginname,adminname)){
        cout << "Admin name was given. Give password to terminate program. \n";
        cin >> temppassword;
        if (!strcmp(temppassword,adminpass)){
                cout << "Admin password right! \n" << "Terminating program.\n";
                return 0;
        }
        cout << "Wrong password!";
        return -1;
    }
    for (int k=0;k<=(totusers-2);k++){
        if (!(strcmp(Obj.getuser(k).getname(),temploginname))){
            cout << "Give your password. \n";
            cin >> temppassword;
            if (!strcmp((Obj.getuser(k)).getpassword(),temppassword)){
                    cout << "Login successful! \n" << "Welcome user: " << k << endl;
                    return k;
            }
            cout << "Wrong password!";
            return -1;
        }
    }
    cout << "No such user found!";
    return -2;
}

void User::addfriend(int totusers){ //In addfriend function the argument totusers is the number of total users + 1 (last user is actually the administrator).
    if (friendsnum > 9){
        cout << "Friends list is full! \n";
        return;
    }
    int tempid;
    cout << "Please enter friend's id number \n";
    cin >> tempid;
    if (tempid <= 0 || tempid > totusers){ //The id given from input is out of range.
        cout << "Invalid id \n";
        return;
    }
    friends[friendsnum]=tempid;
    friendsnum++;
}

void User::delfriend(){
    if (friendsnum == 0){
        cout << "Friend's list is empty! \n";
        return;
    }
    int tempid;
    cout << "Which friend do you want to delete? \n";
    cin >> tempid;
    int counter=-1;
    for(int k=0;k<friendsnum;k++){
        if (friends[k]==tempid){
            friends[k]=friends[friendsnum-1];
            k--;
            friendsnum--;
            counter++;
        }
    }
    if (counter==-1){
        cout << "You have no such friend! \n";
    }
    else{
        cout << counter+1 << " friends deleted. \n";
    }
}

void User::printfriends() const{
    if (friendsnum==0){
        cout << "Friend's list is empty! \n";
        return;
    }
    for (int k=0;k<friendsnum;k++){
        cout << k+1 << ": " << getname() << endl;
    }
}

void searchuser(userscloud Obj,int totusers){
    char tempname[31];

    cout << "Give the name of the user. \n";
    cin >> tempname;
    for (int k=0;k<=(totusers-1);k++){
        if (!(strcmp((Obj.getuser(k)).getname(),tempname))){
            cout << "Requested user found with id: " << (Obj.getuser(k)).getid() << endl;
        }
    }
}

int main()
{
    int newuser = 1;
    userscloud Obj(1); //Create a userscloud object.

    while (1){

        if( !(strcmp(Obj.getuser(newuser-1).getname(),adminname)) && !(strcmp(Obj.getuser(newuser-1).getpassword(),adminpass))){
            break;
        }
        newuser++;
        userscloud Obj(newuser);
	}
	while (1){
	    int curruser = loginpross(Obj,newuser);
	    if(curruser == 0){
            break;
	    }
	    if (curruser>0){

                char inp;
                cout << "Add friend, Delete friend, Print friends, Search someone \n";
                cin >> inp;
                switch (inp){
                    case 'A': case 'a': Obj.getuser(curruser).addfriend(newuser);
                        break;
                    case 'D': case 'd': Obj.getuser(curruser).delfriend();
                        break;
                    case 'P': case 'p': Obj.getuser(curruser).printfriends();
                        break;
                    case 'S': case 's': searchuser(Obj,newuser);
                        break;
                    default: cout << "Invalid option";
                        break;
                }
        }
    }
}

Give name, login name and password for the new user ( <=30 characters eatch ) 

Segmentation fault