Thread: Example from book - time(NULL) doesn't work

I'm reading a book of Micheal Vine, "C For The Absolute Beginner" (because I am an absolute beginner, actually) and there is this piece of code, which is an example from the book, but it doesn't work.

It is a game where you have to memorize numbers and be able to remember them. It should display the numbers for a while and then clear the screen. The problem is that it doesn't wait for a while. It shows the numbers and clears the screen right away.

Here's the entire code:

Code:

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

int main(void) {

    /* Variable definitions. {{{ */
    char c_Yes_No = '';
    int i_Resp1 = 0;
    int i_Resp2 = 0;
    int i_Resp3 = 0;
    int i_Elapsed_Time = 0;
    int i_Current_Time = 0;
    int i_Random_Number = 0;
    int i_1 = 0;
    int i_2 = 0;
    int i_3 = 0;
    int i_Counter = 0; /* Variable definitions end }}} */

    srand(time(NULL));

    printf("
Jogar o jogo da concentração? (s, n)");
    scanf("%c", &c_Yes_No);

    if (c_Yes_No == 's' || c_Yes_No == 'S') { /* {{{ */
    
        i_1 = rand() % 100;
        i_2 = rand() % 100;
        i_3 = rand() % 100;

        printf("Se concentre nos três números.");
        printf("%d    %d    %d", i_1, i_2, i_3);

        /* This DOES NOT work. */
        do {
            i_Elapsed_Time = time(NULL);
        } while ((i_Elapsed_Time - i_Current_Time) < 3);
        
        /* This work. (I tried this myself. It is not from the book. */
        /* sleep(3); */

        system("clear");

        printf("Digite cada número separado por um espaço: ");
        scanf("%d %d %d", &i_Resp1, &i_Resp2, &i_Resp3);

        if (i_1 == i_Resp1 && i_2 == i_Resp2 && i_3 == i_Resp3) { /* {{{ */
        
            printf("Parabéns! Acertou todos.");
        }
        else {
            printf("Os números corretos eram %d, %d, e %d", i_1, i_2, i_3);
        } /* End child if. }}} */

    } /* End 'if'. }}} */

    return 0;
} /* End of main() function. */

/* 
 * vim:foldmethod=marker foldmarker={{{,}}}
 */

This is the piece of code that should make it wait:

Code:

        /* This DOES NOT work. */
        do {
            i_Elapsed_Time = time(NULL);
        } while ((i_Elapsed_Time - i_Current_Time) < 3);

Of course the 'sleep()' function works. However, I would very much like to understand the piece of code with time(NULL) as shown in the book and if is supposed to work, why it doesn't.

Thanks in advance.