How to make getline command work in a while loop?

Question

I use getline command in a while loop. The command works fine in the first loop. But after the second loop, it just passes the getline commands and doesn't allow me to enter

I tried cin.get and cin.getline but the problem is not fixed

#include <iostream>
#include <string>
#include <fstream>

using namespace std;


int price;

void addItem(){
    string product;
    cout << "Please enter product's name: " << endl;
    getline(cin, product);
    cout << "Please enter product's price: " ;
    cin >> price;
    cout << "You have added " << product << " with a price of $" << price << " to your cart." << endl;
}

int main() {
    char answer = 'y';
    int total = 0;
    while (answer == 'y'){
        addItem();
        total += price;
        cout << "Do you want to add another product (y/n)? " ;
        cin >> answer;
    }
    if (answer != 'y'){
        cout << "Your total is $" << total << endl;
    }
    return 0;

}

It's not a good idea to mix `cin >> ...` and `getline(cin, ...)`. That's where the problem is. The reason it's a problem is that `cin >> ...` **does not read newlines**. So you type 'y' followed by newline but only the 'y' is read. The newline isn't read until you get to the next `getline`. — john, Apr 03 '19 at 08:45

score 0 · Answer 1 · edited Apr 03 '19 at 11:47

0

try

while(cin>>answer && answer !='y'){
    cout<<"enter again \n";
}
cout<<"ok";

edited Apr 03 '19 at 11:47

barbsan

3,418
11
21
28

answered Apr 03 '19 at 08:24

Najmeddine Louhichi

102
5

Try explaining your snippet – Hatted Rooster Apr 03 '19 at 08:26
it will execute the getline command an test if there is an input or not – Najmeddine Louhichi Apr 03 '19 at 08:28
It doesn't compile, as you've implicitly changed the type of `answer`. You're also not deailing with whitespace in `answer`. – john Apr 03 '19 at 08:43
getline always reads a string – Najmeddine Louhichi Apr 03 '19 at 08:51
try while(cin>>answer) instead if you want to read a char – Najmeddine Louhichi Apr 03 '19 at 08:51
@NajmeddineLouhichi Well exactly `getline` reads a string but the OPs code `answer` is a char, And your other suggestion `while (cin >> answer)` just has the same problem as the OPs code, which is the mix of `getline` and `>>`. – john Apr 03 '19 at 09:13
@john thanks now i understand the problem. Can't we just use getline in the while loop like in my first answer and the just test the value of the string answer if it contains or not 'y' – Najmeddine Louhichi Apr 03 '19 at 09:19
@NajmeddineLouhichi That seems reasonable as long as you make it clear that this does something slightly different from what the original code does. – john Apr 03 '19 at 09:26
1

@NajmeddineLouhichi It would seem slightly simpler for the OP to just remove getline and use >> thoughout. – john Apr 03 '19 at 09:27
yes i agree. Thanks for the comments – Najmeddine Louhichi Apr 03 '19 at 09:33
I tried this `while(cin>>answer && answer !='y')` but the code didn't compile. I also tried `getline(cin, answer)` instead of `cin >> answer` but the code automatically break after the first loop although the input is 'y' – Thanh Tong Apr 03 '19 at 13:01

score 0 · Answer 2 · answered Apr 03 '19 at 09:57

Mixing cin >> with getline(cin,...), so you should to avoid it. I assume that you used getline to read product name which contain spaces inside. You could rewrite your code to use only getline which should give you expected behavior:

#include <iostream>
#include <string>
#include <fstream>

using namespace std;


int price = 0;

void addItem(){
  string product{};
  string price_str{};
    cout << "Please enter product's name: " << endl;
        getline(cin, product);
    cout << "Please enter product's price: " ;
    getline(cin,price_str);

    /*CHECK IF price_str is number before calling stoi*/

    price = stoi(price_str);
    cout << "You have added " << product << " with a price of $" << price << " to your cart." << endl;
}

int main() {
    string  answer = "y";
    int total = 0;
    while (answer == "y"){
        addItem();
        total += price;
        cout << "Do you want to add another product (y/n)? " ;
        getline(cin,answer);

    }
    if (answer != "y"){
        cout << "Your total is $" << total << endl;
    }
    return 0;

}

I have found a solution for this. I add `cin.ignore()` after `cin >> answer` and it works perfectly. — Thanh Tong, Apr 03 '19 at 12:59

How to make getline command work in a while loop?

2 Answers2