do while loop repeating cout line twice every loop?

Question

Every time I run my program, the output in the first line of the do while loop repeats itself. So the output "Enter characters to add..." is output twice at the start of each loop. How do I make it only output once every loop repetition?

main file

#include "LinkedList.h"
#include "ListNode.h"
#include "Node.h"
#include <iostream>
#include <stdlib.h>
using namespace std;

LinkedList<char> *setUpSentence() {
    //allocate the linked list objet
    LinkedList<char> *sentence = new LinkedList<char>();
    char ch;
    do {
        cout << "Enter characters to add, enter full stop to finish adding." << endl;
        ch = cin.get();
        sentence->addAtEnd(ch);
    } while (ch != '.');

    return sentence;
}

int main() {

    //call the function, store the returned pointer in sentence variable
    LinkedList<char> *sentence = setUpSentence();

    while(sentence->size > 0) {
        cout << sentence->removeAtFront() << endl;
    }  
    //delete to avoid memory leak
    delete sentence;

}

Unrelated: `LinkedList *sentence = new LinkedList();` is unnecessary, just use `LinkedList sentence;` instead and later return it by value. — Baum mit Augen, Jan 27 '17 at 14:23
Regarding your actual question: Please [edit] your question to provide a [mcve]. — Baum mit Augen, Jan 27 '17 at 14:27
@melpomene He breaks at first occurrence of `.` though, before the newline is read. — Baum mit Augen, Jan 27 '17 at 14:27
@BaummitAugen "the newline"? The program expects input one character at a time, so presumably every second input is `'\n'`. — melpomene, Jan 27 '17 at 14:29
@melpomene Depends. One can also write "Coffee tastes great." on first query. Then there is only one newline. That's why we need an MCVE. (But you are most likely right, I'll probably hammer this. OP can edit if we are wrong.) — Baum mit Augen, Jan 27 '17 at 14:31
@BaummitAugen Yeah, but in that case there'd be a question about lots of "Enter characters to add..." output, not "twice at the start of each loop". :-) — melpomene, Jan 27 '17 at 14:32

score 4 · Accepted Answer · edited May 23 '17 at 10:29

4

The problem is in here ch = cin.get();. It will automatically read whatever left in the input stream. You need to clean it first with this.

edited May 23 '17 at 10:29

Community

1
1

answered Jan 27 '17 at 14:32

cuongptnk

472
3
15

score -1 · Answer 2 · edited May 23 '17 at 12:02

-1

Your program is reading from standard input buffer. Read more about this in "What is the standard input buffer?"

If you wish to repeat "cout" only once, rewrite it as follows:

char ch;
cout <<"char"<<ch<< "Enter characters to add, enter full stop to finish adding." << endl;
do {
    ch = cin.get();
} while (ch != '.');

edited May 23 '17 at 12:02

Community

1
1

answered Jan 27 '17 at 14:40

user3305937

43
5

do while loop repeating cout line twice every loop?

2 Answers2