Почему так ? в функции один ответ в мейне другой?

#include <iostream>
#include <cassert>

float travelTime(float distance, float speed){
assert (distance >0);
assert (speed >0);
float time;
time = distance/speed;
std :: cout << time;
return time;

}

int main(){
float distance, speed;
std :: cout << " distance = ";
std :: cin>>distance;

std :: cout << " speed = ";
std :: cin>>speed;


travelTime(distance,speed);
std :: cout << " \n"<<time;
}