Wait for press enter in C inside a while loop?

Question

I'm writing a C program and I need to wait for the user to press any key to continue. When I use getchar(); it waits for the Enter key to be pressed. But when I use it inside a while loop, it doesn't work. How can I make my code wait for any key to be pressed to continue the loop?

Here is my code sample. I am using GNU/Linux.

#include <stdio.h>
#include<stdlib.h>
int main()
{
    int choice;
    while(1) {
        printf("1.Create Train\n");
        printf("2.Display Train\n");
        printf("3.Insert Bogie into Train\n");
        printf("4.Remove Bogie from Train\n");
        printf("5.Search Bogie into Train\n");
        printf("6.Reverse the Train\n");
        printf("7.Exit");
        printf("\nEnter Your choice : ");
        fflush(stdin);
        scanf("%d",&choice);

        switch(choice)
        {
            case 1:
                printf("Train Created.");
                break;
            case 2:
                printf("Train Displayed.");
                break;
            case 7:
                exit(1);
            default:
                printf("Invalid Input!!!\n");
        }

        printf("Press [Enter] key to continue.\n");
        getchar();
    }

    return 0;
}

i'm using linux.not working. undefined reference to `_getchar' — H.R. Shadhin, Feb 07 '15 at 13:59
It's in `conio.h` I think (and a simple web search would get you there too BTW). — barak manos, Feb 07 '15 at 14:04
I think you must use two `getchar()` instead of one. your previous `\n` read in `getchar()` so you need two of it. — Parham Alvani, Feb 07 '15 at 14:05
@barakmanos I think there is no conio.h on linux. it's windows library. — Parham Alvani, Feb 07 '15 at 14:06
@barakmanos i mention that. i'm using linux not windows. `conio.h` only available on windows. @ParhamAlvani its work. but my question is `fflush(stdin)` why not work before `getchar()` ? — H.R. Shadhin, Feb 07 '15 at 14:09
@TuxBot I think you must put your `fflush(stdin)` before your `getchar()` and after your `scanf()` — Parham Alvani, Feb 07 '15 at 14:13
Just add another `getchar()` after your `scanf` or your `getchar()` and remove the `fflush`. — Spikatrix, Feb 07 '15 at 14:15

score 4 · Accepted Answer · answered Feb 08 '15 at 11:29

If this code (with additional fflush)

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int choice;
    while(1){
        printf("1.Create Train\n");
        // print other options
        printf("\nEnter Your choice : ");
        fflush(stdin);
        scanf("%d", &choice);
        // do something with choice
        // ...
        // ask for ENTER key
        printf("Press [Enter] key to continue.\n");
        fflush(stdin); // option ONE to clean stdin
        getchar(); // wait for ENTER
    }
    return 0;
}

does not work properly.

Try this code (with loop):

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int choice;
    while(1){
        printf("1.Create Train\n");
        // print other options
        printf("\nEnter Your choice : ");
        fflush(stdin);
        scanf("%d", &choice);
        // do something with choice
        // ...
        // ask for ENTER key
        printf("Press [Enter] key to continue.\n");
        while(getchar()!='\n'); // option TWO to clean stdin
        getchar(); // wait for ENTER
    }
    return 0;
}

`fflush(stdin)` is Undefined Behavior and should never be used! — alx - recommends codidact, Apr 02 '19 at 22:52
@CacahueteFrito agree (it was in the original code), so option 2 is preferable - `while(getchar()!='\n');` — VolAnd, Apr 03 '19 at 06:17
But it still has a `fflush(stdin)` in the middle. Did you forget to remove it? — alx - recommends codidact, Apr 03 '19 at 07:58
I would put two consecutive `while (getchar() != '\n');` in the end and remove the plain `getchar();`. Then you can remove that `fflush(stdin)` in the middle. — alx - recommends codidact, Apr 03 '19 at 14:08

score 0 · Answer 2 · edited May 23 '17 at 11:45

0

Your answer why fflush(stdin) will not work you can find here:

How to clear input buffer in C?

http://c-faq.com/stdio/stdinflush.html

Hope this helps.

edited May 23 '17 at 11:45

Community

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answered Feb 07 '15 at 14:16

Deepesh

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score 0 · Answer 3 · edited Mar 17 '15 at 05:33

0

getchar() will read the input key pressed by you after entering your choice. In this case Enter key ASCII 13 is read by getchar()

So you need to clear the input buffer or you can use other alternatives.

Alternative 1: use getchar() twice

{
    getchar(); // This will store the enter key
    getchar(); //This will get the character you press..hence wait for the key press

}

edited Mar 17 '15 at 05:33

udondan

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answered Feb 07 '15 at 14:31

Nitin Pandey

649
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Double `getchar()` could not always work. E.g. if user enter string like "1abc" and press Enter (when asked for number). – VolAnd Feb 07 '15 at 15:58

Wait for press enter in C inside a while loop?

3 Answers3

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