Thread: Getchar, getch and gets inside while loop

- I have a if statement. Inside I have a while loop. I've noticed that in the first iteration gets() recieves something without me typing anything(I think it's the previous \n from getchar()). In the second iteration though it works properly. But if I use scanf() it works the first time. WHY?! I need to use gets() so this is really ........ing me off!

- Also the the getchar() inside the while gets ignored. If I put two getchar() together it works. It also works if I put a getch(). WHY!?

Here's my code:

Code:

int bonusRound1()
{
    char y_or_n, firstAns[50], ans[50], exit[]="exit", quit[]="quit", yes[]="y", no[] = "n", nl;
    int i, bonusPoints=0, correctAns=0;
    char charlie[] = "charlie";


printf("\n Would you like to play a bonus round? y or n? ");
y_or_n=getchar();


if(y_or_n == 'y')
{
while(correctAns != 1)
{
    printf("\n________________________________________________________________________________\n");
    printf(" Bonus question 1. Who's quote is this?\n");


    printf("\n \"It's French, the French are coming! I've never been so happy to hear the\n"
           " French.\"\n");
    printf("\n > ");
    //gets(firstAns);
    scanf(" %s", firstAns);
     


    for(i=0; i<=strlen(firstAns); i++)
    {
        ans[i] = tolower(firstAns[i]);
    }


    if(strcmp(ans, charlie) == 0)
    {
        printf("\n That's correct! Press enter to continue...\n");
        //getchar();
        //getchar();
        getch();
        bonusPoints += 10;
        correctAns=1;
    }
    else if(strcmp(ans, quit) == 0 || strcmp(ans, exit) == 0)
    {
        break;
    }


    else
    {
        printf("\n That's incorrect! Press enter to continue...");
        //getchar();
        //getchar();
        getch();
        continue;
    }
}
}
if(y_or_n == 'n')
{
    return;
}


}

gets shouldn't be used because it doesn't check to see how much you type. What it does do though is take the newline out of the input stream. It doesn't keep it, it just throws it out when it stops looking for input (that's how it decides to stop).

gets is basically this:

Code:

gets( string )
    x = 0
    while ( c = getchar ) != \n
        string[ x++ ] = c
    string[ x ] = \0

It doesn't care how much space you've set aside for your string. It just keeps going until it hits a newline.

getchar reads 1 character. So if you type 'c' and hit enter to send that, then your getchar takes the 'c', and the enter key sits there waiting for you to do something with it.


Quzah.

Dont ever use gets() for any reason. Use fgets() instead.

When you use getchar() to input a character you need to make sure you discard the return key, otherwise it will remain in the input buffer and be used by whatever read input function you are using next.

Type faster, noobs!


Quzah.

Originally Posted by sampleandhold

But can someone explain to me why I have to use several getchar() ?!?

It's been explained three times now.

getchar reads 1 character. You are putting in TWO characters (letter + enter key). Why is that confusing to you?


Quzah.

Originally Posted by smokeyangel

Because of the hanging newline from this input:

Code:

 scanf(" %s", firstAns);

Whichever way you go you'll always have a spare newline waiting on stdin by the time you get to your getchar(). getchar() blocks until a newline is entered, so you hit enter here as prompted, and then have 2 newlines to get through.

getch() I'm not so familiar with -- on Windows at least it seems to process the character straight away (no need to press enter at all). The second '\n' is still there, it's just processed less aggressively. If you put getch() followed by getchar() the second getchar() will go straight through with a newline, So, if you use fgets() beforehand to read the answer, then you'll only need one getchar().

You don't have any handling for if the user decides to type in some characters before hitting enter. That'd screw everything up again, so it might be a good idea to loop until getchar() == '\n'. It's all a bit of a headache, but so long as you remember to grab the newlines right after you've typed them it's not so bad

In case the user decides to type in some characters what kind of loop should I use catch all the characters and the \n ? Can you show me how to do it?