Distance, speed, and time calculator. Measure time taken with certain distance and speed, or get the speed needed to travel a certain distance within a certain time.

dst.c

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

#define PROGRAM_NAME "dst"
#define AUTHOR "Daniel H. Hemmingsen"

typedef enum {FALSE, TRUE} BOOLEAN;

/*
 * distance = speed * time
 * speed    = distance / time
 * time     = distance / speed
 */
BOOLEAN calculate(double *distance, double *speed, double *time)
{
	if (*distance <= 0 && *speed > 0 && *time > 0) {
		printf("Calculating distance...\n");
		*distance = *speed * *time;
	} else if (*distance > 0 && *speed <= 0 && *time > 0) {
		printf("Calculating speed...\n");
		*speed = *distance / *time;
	} else if (*distance > 0 && *time <= 0 && *speed > 0) {
		printf("Calculating time...\n");
		*time = *distance / *speed;
	} else {
		return FALSE;
	}

	return TRUE;
}

BOOLEAN human_time(double *time, int *hours, int *minutes, int *seconds)
{
	*seconds = *time * 60 * 60;

	if (*seconds >= 60) {
		while (*seconds >= 60) {
			*seconds = *seconds - 60;
			*minutes = *minutes + 1;
		}
	}

	if (*minutes >= 60) {
		while (*minutes >= 60) {
			*minutes = *minutes - 60;
			*hours = *hours + 1;
		}
	}


	return TRUE;

}

void usage(char *executable)
{
	printf("Usage: %s distance speed time\n\n", executable);
	printf("You need to at least know two of the three values.\n");
	printf("Simply use 0 if you don't know the value.\n\n");
	printf("Example: %s 10 30 0\n", executable);
}
	
int main(int argc, char *argv[])
{
	double distance, speed, time;
	int hours, minutes, seconds;
	BOOLEAN success;

	if (argc != 4) {
		usage(argv[0]);
		return EXIT_FAILURE;
	}

	distance = atof(argv[1]);
	speed = atof(argv[2]);
	time = atof(argv[3]);

	success = calculate(&distance, &speed, &time);

	if (success) {
		printf("Calculation is done...\n\n");
		printf("Distance:\t%.2f km.\n", distance);
		printf("Speed:\t\t%.2f km/h.\n", speed);
	} else {
		usage(argv[0]);
		return EXIT_FAILURE;
	}

	success = human_time(&time, &hours, &minutes, &seconds);

	if (success) {
		printf("\nHuman Readable Time (H:M:S)\n\n");
		printf("%d:%d:%d\n", hours, minutes, seconds);
	} else {
		printf("\n\nCouldn't Calculate Human Readable Time (H:M:S)\n\n");
	
	}

	return EXIT_SUCCESS;
}