How to get user input in do/while loop?

Question

I tried to use the do / while loop I asked about and fixed in my one function in int main to allow the entire program to be rerun if the user wants to, but it is rerunning the program without waiting for user input.

int main()
{
    int spoolnumber = 0;     // Number of spools to be ordered
    float subtotalspool = 0; // Spool sub total
    float shippingcost = 0;  // Shipping cost
    float totalcost = 0;     // Total cost
    char type = 'n';

    do {
        instruct();                     // Print instructions to user
        spoolnumber = spoolnum();       // calculate and store number of spools

        subtotalspool = stotalspool(spoolnumber);       // Calculate subtotal
        shippingcost = shipcost(subtotalspool);         // Calculate subtotal
        totalcost = tcost(subtotalspool, shippingcost); // Calculate final total

        // Print final output
        results(spoolnumber, subtotalspool, shippingcost, totalcost);     
        cout << "\n" << " Would you like to run the program again? [y/n]"; 
    }
    while (type != 'y');

    return 0;
}

Robᵩ · Accepted Answer · 2011-10-17 14:27:01Z

8

You haven't added any code to accept user input. At the bottom of your loop, trying reading a character from cin into type.

Also, you may need to flush the output of cout first, before accepting the user input from cin.

answered Oct 17, 2011 at 14:27

Robᵩ

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Comments

Flexo - Save the data dump · Accepted Answer · 2011-10-17 14:39:28Z

8

You haven't read any input from the user. You could simply do:

cin >> type;

But really you want to be checking that it is succeeding too, e.g. not eof or other errors otherwise it's still possible to loop forever if the user pressed Crtl-D for example.

Checking if it succeeds:

if (!(cin >> type)) {
   // Reading failed
   cerr << "Failed to read input" << endl;
   return -1;
}

Which you could actually make part of the loop condition:

while (cin >> type && type != 'y');

The advice from Xeo about calling cin.ignore() is important to since you will almost certainly end up with more than just one char worth of input.

edited Oct 17, 2011 at 14:39

answered Oct 17, 2011 at 14:27

Flexo - Save the data dump♦

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3 Comments

Sam LaManna Over a year ago

Duh thanks i missed that line. What do you mean checking that it is succeeding?

Xeo Over a year ago

@awoodland: It's not so much about receiving more than one character of input, it's there to remove the trailing \n newline from pressing enter. Thinking again, yeah, that could count as an additional input character. :)

Flexo - Save the data dump Over a year ago

@Xeo - \n was the "almost certainly" extra input I had in mind. I'm not sure that every conforming implementation will give \n and only \n extra if no extra keys are pressed though so the weasel wording was intended as back covering :)

Xeo · Accepted Answer · 2011-10-17 14:41:45Z

6

Well, you never ask for input, do you? Add the following after the cout line:

cin >> type;
cin.ignore(); // remove trailing newline token from pressing [Enter]

Now, you'll still need the usual testing, if the input was valid at all etc, but this should get you going.

edited Oct 17, 2011 at 14:41

answered Oct 17, 2011 at 14:27

Xeo

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Comments

user195488 · Accepted Answer · 2011-10-17 14:27:40Z

2

You need to include a cin in order to retrieve user's decision:

For example:

cout << "\n" << " Would you like to run the program again? [y/n]"; 
cin >> someVariable;

answered Oct 17, 2011 at 14:27

user195488

Comments

Nate · Accepted Answer · 2011-10-17 14:28:10Z

2

That's because you're not prompting the user for input.

You'll be more successful if you try something like:

cout << "\n" << " Would you like to run the program again? [y/n]"; 
cin >> type;

answered Oct 17, 2011 at 14:28

Nate

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