reaction timer test thing

react.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include <termios.h>
#include <ctype.h>
#include <stdbool.h>

int timeval_subtract(struct timeval *result, struct timeval *t2, struct timeval *t1) {
    long int diff = (t2->tv_usec + 1000000 * t2->tv_sec) - (t1->tv_usec + 1000000 * t1->tv_sec);
    result->tv_sec = diff / 1000000;
    result->tv_usec = diff % 1000000;

    return (diff<0);
}

void p_elapsedtime(struct timeval *tv){
    printf("\n%ld.%06lds\n\n", tv->tv_sec, tv->tv_usec);
}

void setterm() {
    struct termios info;
    tcgetattr(0, &info);
    info.c_lflag &= ~ICANON;
    info.c_cc[VMIN] = 1;
    info.c_cc[VTIME] = 0;
    tcsetattr(0, TCSANOW, &info);
}

bool play(double *average, int *times) {
    (*times)++;

    struct timeval tvBegin, tvEnd, tvDiff;
    int r = (rand() % 10) + 5;

    puts("Press any key to start, or press 'q' to exit.");
    if(toupper(getchar()) == 'Q') return false;

    usleep(r * 100000);

    puts("\nPress any key to end the timer!");
    gettimeofday(&tvBegin, NULL);

    getchar();
    gettimeofday(&tvEnd, NULL);

    timeval_subtract(&tvDiff, &tvEnd, &tvBegin);
    p_elapsedtime(&tvDiff);
    *average = *times == 1
        ? (tvDiff.tv_sec + (double)((double)tvDiff.tv_usec / 1000000))
        : ((*average * (*times-1) / *times) + (double)(tvDiff.tv_sec + (double)((double)tvDiff.tv_usec / 1000000))/ * times);
}

int main(int argc, char *argv[]) {
    srand(time(NULL));
    setterm();
    double average = 0;
    int times = 0;

    while(play(&average, &times));

    printf("\n\nAverage: %.6fs\n", average);
    return 0;
}