Step 1 of 5

Reading input in a loop

This module opens Java Programming II, the second half of the course. It has nothing new in it: it's a warm-up. Module 29 ended with a list of everything parts 1 to 7 covered, and this module puts that list to work. Each step reminds you of one group of tools and names the module that taught them, works through an example or two, and then gives you three challenges. If a tool feels rusty, the module named next to it has the full story.

The tools

Tool	What it does	Taught in
`scanner.nextLine()`	reads one line of input as a String	module 2, Reading input and strings
`Integer.valueOf(line)`	turns text such as `"42"` into the int 42	module 3, Variables and types
`/` between two ints	whole-number division: the decimals are dropped	module 4, Calculating with numbers
`%`	the remainder: what's left over after the division	module 6, Conditions and logic
`if`, `else if`, `else`	picks one branch	module 5, Making decisions
`while (true)` and `break`	repeats until something inside the loop ends it	module 8, Repeating with while
`continue`	skips the rest of this round, and goes on with the next one	module 8, Repeating with while
`for (int i = 0; i < n; i++)`	repeats a known number of times	module 9, Loop conditions and for

A worked example

A small car ferry crosses a lake. Its deck holds 4 cars, and bikes ride along in a rack of their own. Before the first crossing, the ferry worker counts the waiting vehicles: the first line of input is how many there are, and each line after it is one vehicle, car or bike. A car's fare is 12 euros, and a bike's 3.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int vehicles = Integer.valueOf(scanner.nextLine());
        int cars = 0;
        int bikes = 0;
        for (int i = 0; i < vehicles; i++) {
            String vehicle = scanner.nextLine();
            if (vehicle.equals("car")) {
                cars++;
            } else {
                bikes++;
            }
        }
        int fullTrips = cars / 4;
        int lastTrip = cars % 4;
        System.out.println("Cars: " + cars + ", bikes: " + bikes);
        System.out.println("Fares: " + (cars * 12 + bikes * 3) + " euros");
        if (lastTrip == 0) {
            System.out.println("Trips: " + fullTrips);
        } else {
            System.out.println("Trips: " + (fullTrips + 1) + ", the last one with " + lastTrip + " cars");
        }
    }
}

Input

8
car
car
bike
car
car
bike
car
car

Output

Cars: 6, bikes: 2
Fares: 78 euros
Trips: 2, the last one with 2 cars

The first line says how many lines follow, so a for loop reads exactly that many, and no stop word is needed. The loop variable i only counts the rounds.
cars / 4 is the number of full trips: with two ints, the division drops the decimals, so 6 cars make 1 full trip, not 1.5. cars % 4 is what's left over, the cars on a last trip that isn't full. When it's 0, every trip is full.
(cars * 12 + bikes * 3) needs its parentheses. Without them, + would join each number to the text in turn instead of adding them up (module 4).

The other common way to read input, until a stop word, with a rule that skips values and counts that grow as the loop goes, is module 29's step "Statistics from input". The first challenge below practices it.

Reading input in a loop

The tools

A worked example

Your task

Challenge 2

Challenge 3