Reading a value with a timer in C

Question

I am writing a multiplication table program to help my niece learn. I want her to be able to have a set amount of time to answer each question (hence the for loop which acts as a delay). The delay works, as after delay seconds the program outputs 'Time's up'! However, the program still waits for me to input a value and press enter before it evaluates answer and checks if it is 'correct' or 'wrong'(this isn't fixed by putting the printf and scanf after the for loop together inside the loop). I know the delay just waits a few seconds and then continues as normal, which is why I need to input a number and press enter. However, I don't know how to get around this.

Basically, I want the program to automatically 'enter' if delay seconds has passed and she hasn't entered a value, resulting in the answer being 'wrong'. But if she enters a value and presses enter before the delay seconds is over, I want to still check if it is either 'correct' or 'wrong'. I have searched for other means of doing this but I simply can't get it right. This is the code so far (again, I know the for loop delay only lets the program wait delay seconds before continuing normally, but I don't know to get around this.

time_t start_time = 0;
int delay = 0;
int answer = 0;
int correct = 0;
int wrong = 0;

printf("How long should the delay be?:\t");
scanf("%d", &delay);

start_time = clock();
printf("\n2 x 4 =\t");

for( ;clock() - start_time <= delay*CLOCKS_PER_SEC; );

printf("\n\nTime's up!\n\n");
scanf("%d", &answer);

if(answer == 8)
{
    printf("\nCorrect!\n");
    ++correct;
}
else if(answer != 8)
{
    printf("\n\aWrong!\n");
    ++wrong;
}

EDIT: I am running Windows and using CodeBlocks with mingw32. I just want the program to be a simple .exe file which will run through CMD. (It does that already though).

Answer 1

Your objective cannot be achieved with scanf() as it is a blocking call - Next code line will not be executed until user enters the input. This is not what you want.

You can use another library function kbhit() - It returns > 0 if any key is pressed. But it won't give you which key is pressed. For that you have to call getch().

kbhit is part of conio.h

So your code would be:

bool bAnswered = false;
for( ;clock() - start_time <= delay*CLOCKS_PER_SEC; )
{
     if(kbhit() > 0)  //Some key is pressed
       {
           answer = getch(); //Read that key
           bAnswered = true; // User has answered 
       }
}

// Print message if there wasn't any key press.
if(bAnswered == false)
{
printf("\n\nTime's up!\n\n");
}

if(answer == 8)
{
    printf("\nCorrect!\n");
    ++correct;
}
else if(answer != 8)
{
    printf("\n\aWrong!\n");
    ++wrong;
}

Problem with above code is you can read only 1 character at a time. I leave that to you for implementing. Also, You need to write additional code to convert ASCII to integer as getch() returns ASCII character.

Answer 2

This mostly works. I cannot test the case when the user starts typing and then the timeout expires. I think it should work in Windows but I can only test under Windows emulation which is less than ideal. User may have to press backspace before typing in the next answer.

#include <windows.h>
#include <process.h>
#include <stdio.h>
#include <stdlib.h>

int answer = 0;

DWORD WINAPIinput_thread(void*) 
{
    scanf("%d", &answer);
    return 0;
}

int main()
{
    srand(time(0));

    HANDLE h = (HANDLE)_beginthreadex(0, 5000, input_thread, 0, 0, 0);
    while (1) {
        int u = rand() % 7 + 2;
        int v = rand() % 7 + 2;
        printf ("%d * %d = ?   ", u, v);

        DWORD res = WaitForSingleObject(h, 20000);

        if (res == WAIT_TIMEOUT)
        {
            printf ("\nSorry, timed out!\n");
            FlushConsoleInputBuffer(GetStdHandle(STD_INPUT_HANDLE));
        }
        else
        {
            if (answer == u * v)
            {
                printf ("Congrats, you won!\n");
            }
            else
            {
                printf ("Sorry, wrong answer!\n");
            }
            CloseHandle(h);
            h = (HANDLE)_beginthreadex(0, 5000, input_thread, 0, 0, 0);
        }
    }

}

Answer 3

Thank you for spending time making sure your niece learns math! A skill we all need more of.

https://gist.github.com/DaemonDave/b2eda8f9fa6b8bbf90a5e1fc1147a461

<script src="https://gist.github.com/DaemonDave/b2eda8f9fa6b8bbf90a5e1fc1147a461.js"></script>

Here is a working math-tester.c file that works on Ubuntu Linux with GCC. You don't need conio, I found a function.

I use 3 things to achieve changes to your requirements. I use kbhit to test for characters to check, I use sleep to wait for second intervals in a while loop, and I use input from command line to ask for the time delay in seconds.

Enjoy!