Unable to Process Data from Text File in C++ - c++

Question

Why is it that this program will not register the correct ID and Pin number entered?
Anything typed will proceed to wrong data being input but the correct data doesn't get recognized.
Inside the text file is 5 IDs, and 5 Pin numbers in a format of 5 rows 2 columns.
#include<iostream>
#include<iomanip>
using namespace std;
void main()
{
const int MAX=10, screenWidth=80;
string A = "Welcome to ABC Bank!";
int i=0;
int ID[MAX], Password[MAX], pin, acc, counter=1 ,limit=2;
cout<<setw((screenWidth-A.size())/2)<<" "<<A<<endl;
cout<<"\nAccount ID: ";
cin>>acc;
cout<<"Pin: ";
cin>>pin;
ifstream accountFile;
accountFile.open("AccountDetails.txt");
if (!accountFile)
cout<<"Unable to open requested file!";
else
{
while (!accountFile.eof())
{
accountFile>>ID[i]>>Password[i];
i++;
}
accountFile.close();
while (acc==ID[i] && pin==Password[i])
{
cout<<"Login successful!\n";
break;
}
while (acc!=ID[i] || pin!=Password[i])
{
if (counter==3)
{
cout<<"\nUnauthorized Access Detected. Account has been LOCKED!\n";
break;
}
else
{
cout<<"\nWrong Account ID/Pin. Please try again!"<<" (Attempts Left:"<<limit<<")";
cout<<"\nAccount ID: ";
cin>>acc;
cout<<"Pin: ";
cin>>pin;
counter++;
limit--;
}
}
}
system("pause");
}
After reviewing what #Joachim Pileborg stated in his answer earlier,
this is the updated code that I have done. Sadly, now this code fails to login successfully after the 1st attempt fails and the 2nd attempt is correct.
ifstream accountFile;
accountFile.open("AccountDetails.txt");
if (!accountFile)
cout<<"Unable to open requested file!";
else
{
while (accountFile>>ID[i]>>Password[i])
{
i++;
}
accountFile.close();
bool success = false;
for (int j=0; !success && j<i; j++)
{
if (ID[j] == acc && Password[j] == pin)
success = true;
}
if (success)
cout<<"\nLogin Successful!\n";
else
{
while (!success)
{
cout<<"\nAccount ID/Pin is incorrect. Please try again!"<<" (Attempts Left: "<<limit<<" )";
cout<<"\nAccount ID: ";
cin>>acc;
cout<<"Pin: ";
cin>>pin;
counter++;
limit--;
if (counter==3)
{
cout<<"Unauthorized Access Detected! Account Has Been LOCKED!\n";
break;
}
}
}
}
system("pause");

Answer 1

The logic for your login success/failure checks are flawed. To begin with they will invoke undefined behavior because you will access uninitialized elements of the arrays.
If, as you say, the file contains five entries, then after the loop i will have the value 5 which is the sixth element in the arrays (after you fix the reading loop, otherwise the value of i will be 6).
If we then overlook the UB (Undefined Behavior) the first loop, checking for successful login, that condition will most likely never be true, and that's good because otherwise you would have an infinite loop there. Then comes the second loop where you check for unsuccessful login, where the condition will almost always be true, and that will lead to an infinite loop.
To check if the login credentials given by the user was correct or not, I suggest something like
bool success = false;
for (int j = 0; !success && j < i; ++j)
{
if (ID[j] == acc && Password[j] == pin)
{
success = true;
}
}
if (success)
{
// Login successful
}
else
{
// Login failed
}

Answer 2

using namespace std;
int main()
{
const int MAX=10, screenWidth=80;
string A = "Welcome to ABC Bank!";
int i=0;
int ID[MAX], Password[MAX], pin, acc, counter=1 ,limit=2;
cout<<setw((screenWidth-A.size())/2)<<" "<<A<<endl;
cout<<"\nAccount ID: ";
cin>>acc;
cout<<"Pin: ";
cin>>pin;
ifstream accountFile;
accountFile.open("AccountDetails.txt");
if (!accountFile)
cout<<"Unable to open requested file!";
else
{
while (accountFile>>ID[i]>>Password[i])
{
i++;
}
accountFile.close();
bool success = false;
while (!success)
{
for (int j=0; !success && j<i; j++)
{
if (ID[j] == acc && Password[j] == pin)
success = true;
}
if (success)
cout<<"\nLogin Successful!\n";
else
{
cout<<"\nAccount ID/Pin is incorrect. Please try again!"<<" (Attempts Left: "<<limit<<" )";
cout<<"\nAccount ID: ";
cin>>acc;
cout<<"Pin: ";
cin>>pin;
counter++;
limit--;
}
if (counter==4)
{
cout<<"Unauthorized Access Detected! Account Has Been LOCKED!\n";
break;
}
}
}
system("pause");
}
CODE IS WORKING, Thank you for the input and help Mr Joachim Pileborg!