getline() error in C++ when using for loop

Question

I had to write a program to calculate average speed of a car during a trip and I have to prompt the user for the names of the two cities that they were traveling between. That program worked, but the next program we had to write is an addition to the last one, in which the user is prompted for how many times the program should run. I declared a new variable for the number of times the users needs the program to run. However when the program enters the loop it skips the first getline() method (asking for the origin city) and skips directly to the second getline() (method asking for the destination city). I have tried clearing the buffer and declaring the loop differently, but whatever I do the string is still read into the program as an empty string. Just wondering if I made a mistake on something or if I cannot use getline() in this instance.

Using C++ and Codeblocks IDE with the GNU Compiler (I've tried other compilers too)

Anyhow here is the code.

#include <iostream>
#include <iomanip>

using namespace std;

int main()
{
    //Declare Variables
    string orgcity = "";
    string destcity = "";
    int hours = 0;
    double minutes = 0.0;
    int hoursmin = 0;
    int minutesmin = 0;
    int minutesmax = 60;
    double dist = 0.0;
    double totalhours = 0.0;
    double avespeed = 0.0;
    double num1 = 0;

    cout << "How many times would you like to calculate the average speed: ";
    cin >> num1;

    for(num1; num1 > 0; --num1)
    {

    //Collect Data
    cout << "Enter the city of origin: ";
    getline(cin, orgcity);

    cout << "Enter the destination city: ";
    getline(cin, destcity);

    //If Statements and Loops...Start here
    do {
        cout << "Enter the number of hours spent in travel: ";
        cin >> hours;

        if (hours < hoursmin)
            cout << "     Invalid number of hours - must be >= 0" << endl;

    } while (hours < hoursmin);

    do {
    cout << "Enter the number of minutes spent in travel: ";
    cin >> minutes;

    if (minutes >= minutesmax){
    cout <<"     Invalid number of minutes - must be in range 0..59" << endl;
    }
    if (minutes <= minutesmin) {
        cout << "     Invalid number of minutes - must be in range 0..59" << endl;
    }
    } while (minutes >= minutesmax);

    //End Here

    cout << "Enter the distance (in miles) between the two cities: ";
    cin >> dist;
    cout << endl;

    //Formula and Final Prompt
    totalhours = (hours + (minutes / 60.0));
    avespeed = dist / totalhours;

    cout << "The average speed of the vehicle traveling" << endl;
    cout << "between " << orgcity << " and " << destcity << " is " << fixed << setprecision(2) << avespeed << " miles per hour." << endl;
    cout << "-------------------------------------------------------------------------------" << endl;
    }
    return 0;

}

Don't use `double` for the loop counter. Use an integer! (Unless you expect to loop e.g. `3.1415` times?) — Some programmer dude, Sep 30 '13 at 05:22
I had changed that earlier in troubleshooting and forgot to change it back. Thanks for the catch. — Andrew Miller, Sep 30 '13 at 05:25
Is this part of a class? (in the 'school' sense, not the OOP sense :) — kfsone, Sep 30 '13 at 05:26
Yes as part of a basic C++ college lab. May be a bit advanced for a low level high school course, but it was easy other than the buffer clear. — Andrew Miller, Sep 30 '13 at 05:42

score 0 · Accepted Answer · answered Sep 30 '13 at 05:15

0

When you read the number of times the loop should be run, the input operator reads the number, but leaves the newline in the buffer. This means that the first call to getline reads that single newline and nothing more.

To make sure you skip anything after that number, up to and including the newline, you can use e.g.

std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

answered Sep 30 '13 at 05:15

Some programmer dude

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If I clear the buffer after the number the program never enters the loop. Is there anyway to change this? – Andrew Miller Sep 30 '13 at 05:17
Should I chose the numeric limit and stream size? – Andrew Miller Sep 30 '13 at 05:20
@AndrewMiller Then you are doing it wrong. Place the line directly after `cin >> num1;` and before the `for` loop. It should not do anything to either your loop or your `num1` variable. – Some programmer dude Sep 30 '13 at 05:21
it gave me an error saying " 'numeric_limits' is not a member of 'std' " – Andrew Miller Sep 30 '13 at 05:23
@AndrewMiller See e.g. [this reference of `std::numeric_limits`](http://en.cppreference.com/w/cpp/types/numeric_limits). It says that you need to include the `` header file. – Some programmer dude Sep 30 '13 at 05:24

getline() error in C++ when using for loop

1 Answers1