C언어 질문입니다.

#include <stdio.h>
 
int main()
{
	double pos[3];
	double vel[3];
	double t_i = 1;
 
	printf("Initial position r(0) = [x(0) y(0) z(0)] = ");
	scanf("%lf%lf%lf", pos[0], pos[1], pos[2]);
 
	while (t_i != 0)
	{
		printf("\n\tTime interval t_i\t\t= ");
		scanf("%lf", &t_i);
		if (t_i < 0) {
			printf("Please input positive time interval\n");
			continue;
		}
		printf("Velocity\t\t[Vx Vy Vz] = ");
		scanf("%lf%lf%lf", vel[0], vel[1], vel[2]);
 
		for (int i = 0; i < 3; i++) {
			pos[i] = pos[i] + (t_i*vel[i]);
		}
 
		printf("\t\t\tr(%.2f) = [%6.2f%6.2f%6.2f]", t_i, pos[0], pos[1], pos[2]);
	}
 
	return 0;
}