How to use file with integer into an array C++ - c++

Question

My task is to create a program to ensure that unauthorized users cannot get into the system. (This is just a scenario, not the real thing). I was given a text file with 300 numbers on it. The user has to type in the number, if it is not included in the text file access will be denied. If it is included in the text file, access will be granted. The rest will be shown below.
So far this is what I have done
#include <iostream>
#include <fstream>
using namespace std;
bool mySequentialSearch(int data[300], int key, int size)
{
for(int i=0; i<size; i++)
{
if (data[i] == key)
return true;
}
return false;
}
int main()
{
int codes;
string line;
ifstream fin ("SystemAccessCodes.txt");
while (fin>>codes)
{
for(int i=0; i<3; i++)
{
cout<<"\nAttempt "<< i+1 << "/3 : ENTER 4 DIGIT CODE: ";
int ans;
cin>>ans;
if(mySequentialSearch(&codes, ans, 300))
{
cout<<"===================="<<endl;
cout<<" Access Granted "<<endl;
cout<<" Welcome "<<endl;
cout<<"===================="<<endl;
system ("pause");
return 0;
}
else
{
cout<<"\nNot matching! Try Again"<<endl;
}
fin.close();
}
}
system ("pause");
return 0;
}
My problem is I don't know how to use the textfile as an array. And it only reads the first number of the file.
Here is some of the numbers in the file (1450
1452
1454
1456
1458
1460) and the program I built only reads 1450.

Answer 1

Separate reading the codes and checking the user input. It makes no sense to do all that in a single loop.
int codes[300];
for(int i = 0; i < 300 && fin; ++i) {
fin>>codes[i];
}
fin.close();
for(int i=0; i<3; i++)
{
cout<<"\nAttempt "<< i+1 << "/3 : ENTER 4 DIGIT CODE: ";
int ans;
cin>>ans;
if(mySequentialSearch(codes, ans, 300))
{
cout<<"===================="<<endl;
cout<<" Access Granted "<<endl;
cout<<" Welcome "<<endl;
cout<<"===================="<<endl;
system ("pause");
return 0;
}
else
{
cout<<"\nNot matching! Try Again"<<endl;
}
}
The better way in c++ is to use a std::vector<int> instead of the raw array though:
std::vector<int> codes;
int code;
while(fin>>code) {
codes.push_back(code);
}
Instead of your mySequentialSearch() function, you can simply use std::vector::find() then.

Answer 2

Here you go:
I think it would be good to use an unordered_set here. To get that, make sure you use #include <unordered_set>
int codes;
std::string line;
std::ifstream fin("SystemAccessCodes.txt");
//lets use a set.
//Sets cannot contain duplicates. If the number is in the set, it is a valid code.
//it might be a better option to use strings rather than ints as passwords
//(large numbers could cause problems)
std::unordered_set<int> codeset;
//populate the set
while (fin >> codes)
{
codeset.insert(codes);
}
fin.close();
//now run this iteration
for (int i = 0; i < 3; i++)
{
std::cout << "\nAttempt " << i + 1 << "/3 : ENTER 4 DIGIT CODE: ";
int ans;
std::cin >> ans;
//count returns either 0 or 1: 0 if the ans is not in it, 1 if it is
if(codeset.count(ans))
{
std::cout << "====================\n";
std::cout << " Access Granted \n";
std::cout << " Welcome \n";
std::cout << "====================\n";
system("pause");
return 0;
}
else
{
std::cout << "\nNot matching! Try Again" << std::endl;
}
}
system("pause");
return 0;
Notes:
Using "using namespace std" pollutes the global namespace. I prefer to use "std::"
Your mySequentialSearch causes an n^2 runtime of your program. Using sets cuts it down to n (linear).
For more information on sets: http://en.cppreference.com/w/cpp/container/unordered_set
For more information on ifstream: http://en.cppreference.com/w/cpp/io/basic_ifstream
It would probably be a good idea to add some error checking (file doesn't exist, bad input, etc.)