Send output on key press

Question

I wrote a simple C++ program that displays a math table:

#include <iostream>
using namespace std;
int main()
{
    int number, result, var=0;
    cout << "Enter number to generate table:";
    cin >> number;
    while (var < number*10)
    {
        result = number + var;
        cout << "\n" << result;
        var += number;
    }
    cin>>var;
    return 0;
}

So when the user types some digits (like e.g. 22) and hits Enter in the Console Window the table will generate. But I want to show the result instantly as the user types the digits. The user should not be required to hit Enter.

How do I process the input without the user hitting Enter?

We'll need more information. C++ itself has no notion of keypresses. — chris, Jul 26 '13 at 06:04
Can you take a look at [this](http://www.cplusplus.com/forum/general/29137/) — NREZ, Jul 26 '13 at 06:05
This is a console and platform feature. Without knowing what console and/or platform you are using, we wouldn't even know if it was possible. Some consoles don't send any keypresses until you hit enter. (Though you'd have a hard time finding any of those today.) — David Schwartz, Jul 26 '13 at 06:07
Not sure if I understand completely, but you may get the desired effect simply by flushing the buffer (`std::cout << std::endl;`) after producing the output. — jogojapan, Jul 26 '13 at 06:07
You will just limit your output table to single digit number input by doing this. Not preferable it is. — , Jul 26 '13 at 06:12
guys my simple point is i just want to get the keystroke and show the result instantly without hitting Enter , can c++ do that itself or not — MAK, Jul 26 '13 at 06:14
How your program is going to decide whether user finished writing or he wants to add another digit? — Qiu, Jul 26 '13 at 06:24
@Qiu no matter user has finished or still want to adds more for instance user hit 2 so program should show the table of 2 but as he add more digits e.g 22, 25 or 26 then it should show the 22, 25 or 26 table instantly. we have a good Example Like Google instant Suggestion — MAK, Jul 26 '13 at 06:28
See also [This question](http://stackoverflow.com/q/1449324/78845) and [the C++ FAQ Lite](http://www.parashift.com/c++-faq-lite/kbhit.html). — johnsyweb, Jul 26 '13 at 06:36
@MAK, you are talking about console here & Google instant suggestion uses web API, Doesn't it occur to you that it is not possible to do such thing on the console. You could do it for just one input using getch() but after that even if there is another way for it, I think that the output table on the console will not change dynamically with your input entry. — , Jul 26 '13 at 06:37
@AmoghDikshit you are correct in your point of view but the idea is same , when you type for a query in Google gives instant suggestions so i want to do the same as user type digits to generate table program should give instant output — MAK, Jul 26 '13 at 09:22

score 3 · Answer 1 · edited Jul 26 '13 at 06:56

3

getch() from <conio.h>, outputs the ASCII code for the single key that was pressed. You may process the returned value afterwards. Something like this:

#include <conio.h>
#include <ctype.h>
int main()
{
    int myVar = 0;
    myVar = getch();
    if (isdigit(myVar))
    {
        myVar = myVar - '0';
    }
    return 0;
}

The drawback is that getch() will only read 1 key.

edited Jul 26 '13 at 06:56

answered Jul 26 '13 at 06:09

Iosif Murariu

2,019
1
21
27

1

Use my example. Instead of `myVar` use `number`, and if `isdigit(number)` returns `false` you should return and not do the rest of your code. – Iosif Murariu Jul 26 '13 at 06:28
and replace `cin >> number` with `number = getch()` – Iosif Murariu Jul 26 '13 at 06:36
i am getting Error "isdigit was not declared in this scope" – MAK Jul 26 '13 at 06:40
1

`#include` to implement `isdigit` – Jul 26 '13 at 06:48

score 1 · Answer 2 · answered Jul 28 '13 at 19:00

1

for input without Enter key, you may use the getch() function in conio.h.. it takes one input character. if you want input to be displayed (echoed) on console, use getche() kbhit() is another function that can detect any keyboard press..

answered Jul 28 '13 at 19:00

Umar Chaudhary

170
9

score 0 · Answer 3 · answered Jul 26 '13 at 06:09

In VC++ you can implement the same logic for LostFocus()of an item where the particular input(var) is given, but in C++ the cin takes the value from the console on the basis of the Enter key press, if you dont press Enter, then the value is not passed from Console to the pgm

Send output on key press

3 Answers3