Checking for input type fails, C++

Question

I have this code which is supposed to fool-proof the program from users entering something else but an integer. I wrote this code based on several sources online but for some reason it doesn't work.

                int cost;                    
                cin >> cost;

                if (!(cin>>cost)) {
                    cout << "Enter a number: ";
                    cin >> cost;
                    cin.ignore(10000, '\n');
                }

The prompt which is supposed to show up when you enter an incorrect type doesn't appear and the program terminates. I've tried moving around and adding cin.ignore() to other places, I've also tried if(cin.fail()) with no success.

Do you actually mean to have cin >> cost; if (!cin >> cost) ...? — Mats Petersson
– Mats Petersson, Commented Apr 23, 2014 at 18:56

Dimitrios Bouzas · Accepted Answer · 2014-04-23 19:00:39Z

3

do the following:

    int cost;
    cout << "Enter a number: ";                
    if(!(cin >> cost) {
      cin.clear();
      cin.ignore(10000, '\n');
    }

Reason : You have a redundant cin statement.

answered Apr 23, 2014 at 19:00

Dimitrios Bouzas

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Massa · Accepted Answer · 2014-04-23 19:06:48Z

0

you might do like @MatsPetersson and @40two mentioned above, but I would do that this way:

const int MAX_TRIES = 3;
int cost;
cout << "Enter a number: ";
for( int tries = 0; !(cin >> cost) && (tries < MAX_TRIES); ++tries ) {
  cin.clear();
  cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
  cout << "This is not a number, try again: ";
}

answered Apr 23, 2014 at 19:06

Massa

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3 Comments

crashmstr Over a year ago

Remember, there is no "above" with answers, as the order can change based on sorting and votes. Instead, you can link to the answers.

Mats Petersson Over a year ago

After the loop, you need something to determine that "tries" ran out and there is still "no good answer"...

Massa Over a year ago

@MatsPetersson if( cin ) { /* cost has a number */ } else { /* boohoo */ } :D

DesignIsLife · Accepted Answer · 2014-04-24 09:29:53Z

0

Should work like this,

int cost; 
while (!(cin >> cost) 
{  
  cout << "Enter a number:";  
  cin.ignore(10000, '\n');   
}

edited Apr 24, 2014 at 9:29

answered Apr 23, 2014 at 19:04

DesignIsLife

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