why does getchar in while not execute after first iteration?

Question

I wrote a program to read from input character by character and print it to output and here is my code:

#include <stdio.h>

main()
{

    int c;
    while((c = getchar()) != EOF)
    {
        printf("%s\n", "log1");
        printf("%c\n", c);
        printf("%s\n", "log2");
    }

}

and this is the result:

a(my input)
log1
a
log2
log1


log2

but it should have this result:

a
log1
a
log2

what's wrong with this program?

Did you try looking to several hundred related answers on SO, before clicking the "Post Your Question" Button ? — P0W, Oct 13 '13 at 06:14
Are you sure, you don't type in anything else but the character 'a' ? — Aki Suihkonen, Oct 13 '13 at 06:17

score 2 · Accepted Answer · answered Oct 13 '13 at 06:17

you giving input a and newline

a(my input)  You are giving a and newline

//this is because of a 
log1
a
log2 

//this is because of newline
log1


log2

Check for newline and avoid printing Newline.

    while((c = getchar()) != EOF)
        {
            if(c!='\n')
               {  
                printf("%s\n", "log1");
                printf("%c\n", c);
                printf("%s\n", "log2");
               }
        }

score 0 · Answer 2 · edited May 23 '17 at 11:50

0

This is because you while((c = getchar()) != EOF) ends after hitting EOF. This is because when you type something and you hit the enter key then everything is stored in an internal buffer.

Your code stops when getchar doesn't find anything in that buffer.

You may also check out this:- Where does getchar() store the user input?

edited May 23 '17 at 11:50

Community

1
1

answered Oct 13 '13 at 06:17

Rahul Tripathi

168,305
31
280
331

Try pressing Ctrl + D after some input. – Rahul Tripathi Oct 13 '13 at 06:26

score 0 · Answer 3 · answered Oct 13 '13 at 06:18

getchar is running during the second iteration. The problem is that your input was actually "a[enter]", so the second character that getchar read was a newline character, and it printed that.

If you give input of "abc", the things may seem more clear.

score 0 · Answer 4 · answered Oct 13 '13 at 06:27

0

while(getchar() != '\n');

bear in mind that the expression in the while loop is executed everytime - so even when the character is '\n' is found, it has already been removed from the stream by the getchar() call.

answered Oct 13 '13 at 06:27

CodeMonk

920
1
12
22

haccks · Answer 5 · 2013-10-13T09:43:43.563

0

Place a condition not to print \n (on pressing Enter

  while((c = getchar()) != EOF)
        {
            if(c != '\n') 
            printf("%s\n", "log1");
            printf("%c\n", c);
            printf("%s\n", "log2");
        }

edited Oct 13 '13 at 09:43

answered Oct 13 '13 at 09:38

haccks

104,019
25
176
264

why does getchar in while not execute after first iteration?

5 Answers5

Linked