using user-defined function, do/while loop, to print name

Hi

What's the wrong with the code? When I enter 'n' it exits fine. But when I enter 'y' or any other character the program goes crazy. Please have look at the outputs at the bottom.

Code:

---

// print your name n times

#include <iostream>
#include <cstdlib>
#include <cstring>

using namespace std;

void prntname(int dummy1, string dummy2);

int main()

{
    string name; int n; char ch;

    do
    {
        cout << "enter your name: ";
        getline (cin, name);
        cout << "how many times you want to print?: "; cin >> n;
        prntname(n, name);
        cout << endl;
        cout << "do you want to repeat?: "; cin >> ch;
    }
    while (ch != 'n');

    cout << endl;

    system("pause");

    return 0;
}

//---------------------------------------------------------
// function definition for void prntname(int dummy, string dummy)

void prntname(int dummy1, string dummy2)

{
    for (int j=1; j<=dummy1; j++)
    {
        cout << dummy2 << endl;
    }
}
//------------------------------------------------------------

---

Output when I enter 'n'. The program exits fine:

Code:

---

enter your name: jackson heights
how many times you want to print?: 10
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights

do you want to repeat?: n

Press any key to continue . . .

---

Output when I enter 'y' or any other character. The program goes crazy:

Code:

---

enter your name: jackson heights
how many times you want to print?: 10
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights
jackson heights

do you want to repeat?: y
enter your name: how many times you want to print?:

---

'cin >> ch' has left a newline in the input stream, therefore when 'getline' is called, it terminates immediately.

Quote:

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Originally Posted by Sipher

'cin >> ch' has left a newline in the input stream, therefore when 'getline' is called, it terminates immediately.

---

Thanks, Sipher.

It's the first time I have used getline. I don't know what 'precautions' what needs to take when working with getline. How do I correct that erroneous behavior? Could you please help me? Thank you.

Quote:

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Originally Posted by jackson6612

Thanks, Sipher.

It's the first time I have used getline. I don't know what 'precautions' what needs to take when working with getline. How do I correct that erroneous behavior? Could you please help me? Thank you.

---

It's not getline() that's your issue. It's about datatypes and I/O in general.

'n' is a char.
'y' is a char.
'\n' (the newline) is a char.

When you use that program, you do not just hit 'n' or 'y'. You hit 'n' or 'y', then ENTER, which is '\n', the newline. The 'n' or 'y' gets put into ch.

What do you think happens to the '\n'? It doesn't disappear. It's still there, in the stdin buffer. So the next cin >> ch grabs it.

Quote:

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Originally Posted by MK27

It's not getline() that's your issue. It's about datatypes and I/O in general.

'n' is a char.
'y' is a char.
'\n' (the newline) is a char.

When you use that program, you do not just hit 'n' or 'y'. You hit 'n' or 'y', then ENTER, which is '\n', the newline. The 'n' or 'y' gets put into ch.

What do you think happens to the '\n'? It doesn't disappear. It's still there, in the stdin buffer. So the next cin >> ch grabs it.

---

Thanks, MK27.

I understand it now. But how do I empty that buffer...? Could you please tell me? Thank you.

Code:

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std::cin.flush()

---

If I remember correctly. just call flush() at the beginning of your loop.

Thanks. Unfortunately it isn't working. I have used these combinations: std::cin.flush(), cin.flush(), std::cin.clear(), cin.clear(). But none worked. Please help me.

Code:

---

// print your name n times

#include <iostream>
#include <cstdlib>
#include <cstring>

using namespace std;

void prntname(int dummy1, string dummy2);

int main()

{
    string name; int n; char ch;

    do
    {
        cin.flush();
        cout << "enter your name: ";
        getline (cin, name);
        cout << "how many times you want to print?: "; cin >> n;
        prntname(n, name);
        cout << endl;
        cout << "do you want to repeat?: "; cin >> ch;
    }
    while (ch != 'n');

    cout << endl;

    system("pause");

    return 0;
}

//---------------------------------------------------------
// function definition for void prntname(int dummy, string dummy)

void prntname(int dummy1, string dummy2)

{
    for (int j=1; j<=dummy1; j++)
    {
        cout << dummy2 << endl;
    }
}
//--------------------------------------------------------------

---

try cin.ignore(MAX_INT,'\n') ; or INT_MAX

you can clear the buffer in cin before input just like this ：

Code:

---

// print your name n times

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <string>
using namespace std;

void prntname(int dummy1, string dummy2);

int main()

{
        string name; int n; char ch;

        do
        {
                cin.sync();
                cout << "enter your name: ";
                getline (cin, name);
                cout << "how many times you want to print?: ";
                cin >> n;
                prntname(n, name);
                cout << endl;
                cout << "do you want to repeat?: ";
                cin >> ch;
        }
        while (ch != 'n' && ch);

        cout << endl;

        system("pause");

        return 0;
}
void prntname(int dummy1, string dummy2)

{
        for (int j=1; j<=dummy1; j++)
        {
                cout << dummy2 << endl;
        }
}

---

the test is ok！ you can have a test ！