Why, in this program, does the printf function print or not print depending on where it is inside the loop?

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

int main()
{
    
    char frames[] = {'-', '\', '|', '/'};
    
    int i = 0;
    time_t prev_time = time(0);
    while(1) {
        printf("r%c", frames[i % 4]); //<- when placed here, it will flush
        if (time(0) - prev_time < 1) continue;
        //printf("r%c", frames[i % 4]); <- when placed here, it needs to be manually flushed
        //fflush(stdout);
        prev_time = time(0);
        i++;
    }

    return 0;
}