Increasing an integer through a time delay

Question

I'm producing a game in C on a microprocessor. The score is controlled by how long you can survive; the score increases by 1 every 3 seconds. The score is an integer which is declared globally, but displayed from a function.

int score = 0;//globally declared

void draw_score(int score_d)
{
    char score_draw[99];
    sprintf(score_draw,"%d", score_d);
    draw_string(score_draw, 9, 0);
}

I was thinking of a function which just increases the score by one with a delay on it, however that has not worked.

void score_increaser(int score)
{
    score++;
    _delay_ms( 3000 );
}

Does it need to be in a while loop? the function itself would go into a while loop in the main anyway.

Answer 1

C is pass by value.

score_increaser() as shown in your question increases just a copy of what is passed in.

To fix this there are (mainly) two options:

1. As score is defined globally, do not pass in anything:

   void score_increaser(void) {
     score++;
     _delay_ms( 3000 );
   }
   

   This modifes the globale score directly.

2. Pass in the address of score and de-reference it inside the function

   void score_increaser(int * pscore) {
     (*pscore)++;
     _delay_ms( 3000 );
   }
   

   Call it like this

   ...
   score_increaser(&score);
   ...
   

A 3rd, a bit more complex, approach (which assumes signals are supported on the target platform) would

1. setup a signal and a referring handler, then
2. setup a timer to fire a signal every N seconds.
3. This signal then is handled by the handler, which in turn
4. increases the global score and
5. starts the timer again.

This might look like:

#include <signal.h> /* for signal() and sig_atomic_t */
#include <unistd.h> /* for alarm() */


#define DURATION (3) /* Increase score every 3 seconds. */

sig_atomic_t score = 0;


void set_alarm(unsigned);

void handler_alarm(int sig)
{
  ++score;
  set_alarm(DURATION);
}

void set_alarm(unsigned duration)
{
  signal(SIGALRM, handler_alarm);
  alarm(duration);
}


int main(void)
{
  set_alarm(DURATION);

  ... /* The game's codes here. */
}

This latter approach has the advantage that your game's code does not need to take care about increasing score. score is just increased every 3 seconds as long as the program runs.