Array problem

[jual]

I just started learning C++ this week, and I've been experimenting with different concepts. I wrote the program below to see what happens. Eventually, I want to make a code-breaking game.

#include<iostream>
using namespace std;

int main ()
{
char code[4], guess[4];

cout << "Enter the code: ";
cin >> code;
cout << "Enter the guess: ";
cin >> guess;

cout << code[0];
cout << code[1];
cout << code[2];
cout << code[3] << endl;

cout << guess[0];
cout << guess[1];
cout << guess[2];
cout << guess[3];

return 0;
}

The problem is that the first digit of the code doesn't show up. For example, if I enter '1234' for both code and guess, it will output this:

234
1234

Why doesn't the '1' show up? Any help would be appreciated!

[freddy92]

I have literally no idea why this worked, but when I switched the order that the user inputs the numbers (guess then code), it outputted "1234" for each one.

Edit: just switched the order back and it still works, even though it didn't before. Weird.

[jual]

I just tried that and it worked for me as well. That's strange...

[freddy92]

I have no idea why it wouldn't work before, and I REALLY have no idea why switching the order made it work... lol

[cire]

code and guess both have storage for 4 chars. Using cin>>code and cin>>guess requires storage for 5 chars each (assuming you enter 4-char strings,) so you are trampling memory you don't own.

Welcome to the wild and wonderful world of undefined behavior.

[jual]

I tried switching it back (code then guess) and it didn't work again. 'Guess then code' works fine though. Yes, it is very strange... Thanks for your help though!

[Cubbi]

As cire pointed out, doing cin >> into an array is dangerous. Moreover, because you're not preventing buffer overflow, it makes your program hackable in the worst possible way: a malicious user can trick it to execute arbitrary code.

Either (and very much preferred) use strings:

string code, guess;

cout << "Enter the code: ";
cin >> code;
cout << "Enter the guess: ";
cin >> guess;

Or at least limit the input to the size of your buffers:

char code[4], guess[4];

cout << "Enter the code: ";
cin >> setw(4) >> code;
cin.ignore(1000, '\n'); // in case you entered too much
cout << "Enter the guess: ";
cin >> setw(4) >> guess;

(although you may want to make them code[5] and setw(5), if you want to enter four-characters trings)

[vlad from moscow]

The result

234
1234

is simply explained.

Your declared variables

char code[4], guess[4];

are placed in the memory the following way

guess           code 
[_][_][_][_] [_][_][_][_]

When you entered code the memory become to look the following way

guess           code 
[_][_][_][_] [1][2][3][4] and additional byte for '\0' ['\0']

That there was memory overflow

When you entered guess. The memory become to look the following way

guess           code 
[1][2][3][4] ['\0'][2][3][4] and additional byte for '\0' [0]

The symbol '\0; is not displayable. So you got the result

234
1234

The problem is that you have to declare your arrays as

char code[5], guess[5];

because one byte is required for terminating zero.

[jual]

Thank you for the explanation cire, Cubbi and vlad from moscow. It really helped! I think I'll use strings instead of arrays.