Question

Here is an excerpt of my code, where the problem lies.

    long long user_largest_plus;
    long long user_largest_minus;
    cout << "Input the largest+1 in decimal: " << endl;
    cin >> user_largest_plus;
//cout << endl;


   // cout << "Input the largest-1 in decimal: " << endl;
    cin >> user_largest_minus;
    cout << endl;

    cout << "In decimal plus: " << user_largest_plus;
    cout << endl;
    cout << "In decimal minus: " << user_largest_minus;

As soon as I input 9223372036854775808 to user_largest_plus, the execution would terminate. That is, I wouldn’t be able to input for user_largest_minus.
I am using Code::Blocks, MinGW compiler.

Is it because I just overflowed the variable, and the error triggered this termination. Any work around?

By the way, that number is 2^63 - 1, maximum number that I can store.

Thanks

Answer 1

Try replacing

cin >> user_largest_plus;

with

if( !( cin >> user_largest_plus ) ) {
    user_largest_plus = 0;
    cin.clear();
    cout << "Bad input. Using zero instead\n";
}

When the input text is not a valid long long, two interesting things happen:

• user_largest_plus is never set, and
• the bad bit is set in cin.

The provided code sets some value to user_largest_plus to avoid undefined behavior, and clears the bad bit, so cin can still be used.