why does while loop using cin.get() function outputs result twice?

Question

#include <iostream>
using namespace std;


int main()
{

    int a ;
    while ( ( a = cin.get() ) != EOF )
    {

       cout << "hi" <<endl;

     } // end while


}

I wonder why this outputs "hi" twice whenever I input once.

for example

input : 1 output : hi hi

@PavanChandaka: Why +1? Newline is a char too, part of the OP's input...and _that_'s the problem! — Lightness Races in Orbit, Sep 26 '16 at 23:31
`while( cin >> a) cout << "Hi" << endl` if you want loop to stop while reaching EOF: add inside loop `cin.sync();` — Raindrop7, Sep 26 '16 at 23:34

score 2 · Accepted Answer · answered Sep 26 '16 at 23:16

2

Your input actually consists of two characters: the character 1 followed by a newline.

Try piping in the contents of a file that only contains one byte, or a one-letter string without newline, and you'll see only one "hi".

answered Sep 26 '16 at 23:16

Kerrek SB

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@BaummitAugen: No problem :-) – Kerrek SB Sep 26 '16 at 23:21
just select "enter" key with out entering any value. you will see a "hi". This explains your code takes a "newline" char. – Pavan Chandaka Sep 26 '16 at 23:23
Or turn off line buffering in your terminal emulator – Lightness Races in Orbit Sep 26 '16 at 23:32

score 1 · Answer 2 · answered Sep 26 '16 at 23:38

Add a line of code to print the value of a. That will help you understand what the input values the program sees:

int main()
{
    int a ;
    while ( ( a = cin.get() ) != EOF )
    {
       cout << a << endl;
       cout << "hi" << endl;    
    } // end while    
}

If your systems uses ASCII values for char encoding you can find out what the output means by looking up the ASCII table.

why does while loop using cin.get() function outputs result twice?

2 Answers2