Why is system("clear") command not working the way expected?

Question

#include <stdio.h>
#include <time.h>
#include <stdlib.h>

int main()
{
    int iCurrentTime = 0;
    int iElapsedTime = 0;
    char cYesNo = '\0';
    int i1 = 0;
    int i2 = 0;
    int i3 = 0;
    int iRes1 = 0;
    int iRes2 = 0;
    int iRes3 = 0;
    srand(time(NULL));

    printf("Do you want to play a concentration game? (y or n or 1): ");
    scanf("%c", &cYesNo);

    if(cYesNo == 'y' || cYesNo == 'Y' || cYesNo == '1')
    {
        i1 = (rand() % 99) + 1;
        i2 = (rand() % 99) + 1;
        i3 = (rand() % 99) + 1;

        printf("Concentrate on these numbers:\n\n%d\t%d\t%d", i1, i2, i3);

        iCurrentTime = time(NULL);

        do
        {
            iElapsedTime = time(NULL);
        } while( (iElapsedTime - iCurrentTime) < 3 ); //end do while loop

        system("clear");

        printf("Enter the numbers separated by spaces:\n");
        scanf("%d%d%d", &iRes1, &iRes2, &iRes3);

        if(i1==iRes1 && i2==iRes2 && i3==iRes3)
        {
            printf("Congratulations!!");
        }//end if
        else
        {
            printf("Better luck next time.");
        }
    }//end if

    return 0;
}//end main

I am a high-school student who is new to programming and I borrowed a book from my local library to learn C: "C Programming for the Absolute Beginner".
I copied this code from the book but it does not work for some reason. When I execute it, it should:

• Ask the user if she/he wants to play a concentration game. Accepts "y" or "n" or "1"
• displays three numbers
• Clears the screen after 3 seconds and prompts us for the three numbers.

The first part works just fine.
The second and third parts don't work the way expected. (See the picture)

The screen doesn't clear before prompting us and some numbers on the left that are probably time.

The description of what the program should do according to the book, word-to-word:

The Concentration game uses many of the techniques you learned about in this chapter. As shown in Figure 4.14, the game generates random numbers and displays them for a short period for the user to memorize. While the random numbers are displayed, the player would try to memorize the numbers and their sequence. After a few seconds have passed, the screen is cleared and the user is asked to enter the memorized numbers in the correct sequence.

(sorry I can't give "Figure 4.14")

Answer 1

Here you tell printf() to output four values, but you only provide three.

printf("Concentrate on these numbers:\n\n%d\t%d\t%d\t%d", i1, i2, i3);

You should change that to match the number of given values;

printf("Concentrate on these numbers:\n\n%d\t%d\t%d", i1, i2, i3);

Answer 2

I figured out the problem with your program. Turns out it has nothing to do with clear (which you said you tried and is working anyway) or carriage return or any of that.

The key: you absolutely must end your printf strings with newlines (\n characters).

Especially this line:

printf("Concentrate on these numbers:\n\n%d\t%d\t%d\n", i1, i2, i3);
//                                                 ^^ needs this

Otherwise, the %d\t%d\t%d part of your string is not being flushed to the standard output, at least not immediately. So you are not seeing that part display until after your screen-clear, and even then, not until after the next string you print ("Enter the numbers...") finishes the line with its own \n. Only then does that accumulated string flush to your screen -- because the system prefers to flush full lines, not partial ones (unless you force the fflush(stdout)).

You also need to end your "Congratulations" and "Better luck..." strings with newlines too, or those won't look right either when your program ends.

That should do it!

Prior suggestion:

Unfortunately this doesn't seem like an appropriate program for beginners. Yes it's simple, but it contains some system-specific or compiler-specific things that are giving you behavior that you're not expecting.

First of all, like others have mentioned, you have a printf line specifying a format containing four numerical %d values, to which you are only providing three integer parameters. The fourth "tries" to print, which is that -2143927864 value you see.

Next, the system-related functions like system("clear") don't appear from your screenshot to actually be clearing the screen. Also, time(NULL) may not be returning the "realtime" integer value that you are expecting.

Finally, it even seems like your environment is not treating your newline \n characters consistently, or as your C program intends. Printing this character should move your cursor to the beginning of the next line. However, it may behave differently on different terminal programs on different platforms! \n sometimes performs a combination of actions provided by both "linefeed" (0x0A) and "carriage return" (\r or 0x0D) characters. The latter merely moves your cursor to the beginning of the current line, not the next line, then prints more characters over previously-printed ones. This appears to be what you are seeing.

Answer 3

WRONG : printf("Concentrate on these numbers:\n\n%d\t%d\t%d\t%d", i1, i2, i3); CORRECT :printf("Concentrate on these numbers:\n\n%d\t%d\t%d", i1, i2, i3);

YOU ENTERED EXTRA %d ..

Answer 4

The error is in the below mentioned line.

printf("Concentrate on these numbers:\n\n%d\t%d\t%d\t%d", i1, i2, i3);

You have used four format specifier %d instead of three. The code should be

printf("Concentrate on these numbers:\n\n%d\t%d\t%d", i1, i2, i3);