Transportation C++

Question

/* How to calculate the number of buses i need to transport people? if I enter the number 165, it outputs 3 although it should be 4 */

#include <iostream>
using namespace std;

int main() {
int bus_max = 50;
int passengers;
int last_bus;
int buses;
int free_places;
cout << "Enter the number of passengers: ";
cin >> passengers;
last_bus = passengers % bus_max;
cout << "Last bus will take " << last_bus << " passengers." << endl;
free_places = bus_max - last_bus;
cout << free_places << " free seats will remain." << endl;
buses = passengers / bus_max;
cout << "It will take " << buses << " buses to transport " << passengers << " people." << endl;
system("PAUSE");
return 0;
}

Answer 1

That is because C++ rounds down by default when you divide. You can use functions such as round() and ceil() in <cmath> and <math.h> relatively, to round up, but a simple if statement will also work:

if(last_bus > 0)
buses++;

So this code works fine:

#include <iostream>
using namespace std;

int main() {
int bus_max = 50;
int passengers;
int last_bus;
int buses;
int free_places;
cout << "Enter the number of passengers: ";
cin >> passengers;
last_bus = passengers % bus_max;
cout << "Last bus will take " << last_bus << " passengers." << endl;
free_places = bus_max - last_bus;
cout << free_places << " free seats will remain." << endl;
buses = passengers/bus_max;

if(last_bus > 0)
buses++;

cout << "It will take " << buses << " buses to transport " << passengers << " people." << endl;
system("PAUSE");
return 0;
}

Answer 2

many thanks!

Answer 3

Aleksei Radchenkov explained it well, but I want to dig a little deeper, because C++ doesn't actually round down the result of the division (of integers):

Every CPU (or at least most of them) can deal with 2 kind of numbers: those written in "binary" (integers) and those written in "scientific notation" (floating-point numbers)

When doing operations on integers it gives an integer;
when doing operations with floating-point numbers it gives a floating-point number

So, when doing a division of integers, it performes the Euclidean division (the one with quotient and reminder)
which result tells how many times does A fit in B,
never the "real" division (A times the multiplicative inverse of B) which is performed only on floating-point numbers