AP CSA 1.1 Exercise 1: Step Tracker

Unit 1: Using Objects and Methods · Lesson 1.1 · Exercise 1

Step Tracker

Introduction to Algorithms, Programming, and Compilers. Write real Java, run it, and submit it to be graded against hidden test cases.

Back to the Lesson 1.1 page All Unit 1 lessons

Why this one is worth doing

An algorithm is an ordered sequence of steps, and order is the whole point. This one asks you to report the total after every step, so a step done out of order shows up immediately.

What to write

Read three integers: a starting step count, a number of steps gained, and a number of steps lost.
Print the starting count.
Add the gain, then print the new total.
Subtract the loss, then print the new total.
Print the total one more time, doubled, as a stretch goal for tomorrow.

Your program reads

Three integers on separate lines: start, gained, lost.

Your program prints

Four lines: the start, the total after the gain, the total after the loss, and that final total doubled.

Worked examples

These are the cases you can see. There are more you cannot, and they use different values, so an answer that prints these numbers as constants will fail.

Example 1 input

1000
2500
400

Example 1 output

Example 2 input

0
10
3

Example 2 output

Your answer

Main.java

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    // Reading input is Lesson 1.4. It is written for you here.
    Scanner input = new Scanner(System.in);
    int start = input.nextInt();
    int gained = input.nextInt();
    int lost = input.nextInt();

    // Your algorithm goes here. Four printed lines, in order.
  }
}

Input for the Run button

Run sends whatever is in the input box below. Submitting runs your program against every test case, including hidden ones with different input.

Stuck?

Hint 1

Keep one variable for the running total and change it step by step. Printing start + gained - lost in one line gets the last number right and the middle ones wrong.

Hint 2

System.out.println prints its argument and then moves to a new line. Four calls means four lines.

Hint 3

The order of the printed lines is part of the answer. A correct total printed in the wrong place still fails.

Where to go next

Rework the Lesson 1.1 page Pick another Unit 1 lesson

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