Beats per minute counter using key presses in C

Question

I'm building a C program to determine how many times a key is pressed in one minute (think "beats per minute") so I can use it later in a metronome I'm building.

I want to build something like this in C. How would I read the key presses as they happen?

Answer 1

Use fgetc() to read keypress of the ENTER key.

Use gettimeofday() to measure time in microseconds, compute time elapsed from previous keypress, and divide 60s by it.

#include <sys/time.h>
#include <stdio.h>
#include <string.h>

int main(void)
{
    struct timeval t0, t1;
    float elapsed;
    gettimeofday(&t0, 0);
    while(1) {
        fgetc(stdin);
        gettimeofday(&t1, 0);
        elapsed = (t1.tv_sec - t0.tv_sec) * 1000.0f + (t1.tv_usec - t0.tv_usec) / 1000.0f;
        memcpy(&t0, &t1, sizeof(struct timeval));
        printf("%f\n", 60000./elapsed);
    }
    return 0;
}

You may want to average displayed values (e.g. keep a running average) to reduce variance.