How to check if the input into an array failed?

Question

I'm doing a homework assignment and one function I need to write is a simple function that allows the user to input an int that will go into an array. One of the conditions though is to check if the input failed, and if it did, end the the program with a 'die' function. How do I check if the input was not put into the array? Should I just check that the input was an int? Thanks for the help.

void input( unsigned a[], unsigned elements ){


    for (unsigned i = 0; i < elements; i++) {
        cout << "Enter a number for index #" << i <<" in the array:" << endl;
        cin >> a[i];
    }

    // Add die function if this function fails...

}

bool die(const string &msg) {
    cerr <<endl << "fatal error: " <<msg <<endl;
    exit( EXIT_FAILURE );
}

Why don't you input as a string, then check if the string is a valid number. — OldProgrammer
– OldProgrammer, Commented Feb 21, 2013 at 22:37
The function prototype has to be the same as the professor's. — user1681673
– user1681673, Commented Feb 21, 2013 at 22:39
possible duplicate of The Definitive C++ Book Guide and List — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Feb 21, 2013 at 22:42
well, you could iterate through array for the value of i or utilize try and catch in some way. Since it is homework, I do not want to be specific. — Benjamin Trent
– Benjamin Trent, Commented Feb 21, 2013 at 22:42

Kerrek SB · Accepted Answer · 2013-02-21 22:41:43Z

2

Like this:

if (!(cin >> a[i])) { die("boo"); }

answered Feb 21, 2013 at 22:41

Kerrek SB

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5 Comments

user1681673 Over a year ago

What if the input was zero?

leemes Over a year ago

Well, zero is a valid input, isn't it? (It is an unsigned integer)

user1681673 Over a year ago

Ok, I was just checking. I've used (!(statement)) in the past but may be unsure of exactly what it means. I thought it meant "if input was zero." Is that wrong? Thanks for the help.

Kerrek SB Over a year ago

@user1681673: The result of cin >> a[i] is the stream object, not the integer. So you're testing whether the stream has failed. Only if the stream is still good are you even allowed to touch the integer.

user1681673 Over a year ago

OH. So it's checking whether or not a stream occurred. Got it. Thanks for the help.

user2116846 · Accepted Answer · 2017-02-20 16:32:48Z

0

void input( unsigned a[], unsigned elements ) {

for (unsigned i = 0; i < elements; i++) {
    cout << "Enter a number for index #" << i <<" in the array:" << endl;
    cin >> a[i] || die("Error");
}

answered Feb 20, 2017 at 16:32

user2116846

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