Arrays Code Practice

Activity 4.20.1.

Fix the following code so that it prints every other value in the array arr1 starting with the value at index 0.

public class Test1
{
    public static void main(String[] args)
    {
        int arr1 = {1, 3, 7, 9, 15, 17};
        for (int index = 0; index <= arr1.length; index += 2)
        {
            System.out.print(index + ", ");
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "1, 7, 15, ";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testCodeContains1()
    {
        boolean passed = checkCodeContains("correct array data type", "int[] arr1");
        assertTrue(passed);
    }

@Test
    public void testCodeContains2()
    {
        boolean passed =
                checkCodeContains(
                        "correct for loop condition",
                        "for (int index = 0; index < arr1.length; index+=2)");
        assertTrue(passed);
    }

@Test
    public void testCodeContains3()
    {
        boolean passed =
                checkCodeContains(
                        "access values in array instead of index",
                        "System.out.print(arr1[index] + \", \")");
        assertTrue(passed);
    }
}

Activity 4.20.2.

Fix the following to print the values in the array a1 starting with the value at the last index and then backwards to the value at the first index.

public class Test1
{
    public static void main(String[] args)
    {
        int[] a1 = {1, 3, 7, 9, 15};
        for (int i = a1.length; i > 0; i--)
        {
            System.out.print(arr[i] + ", ");
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "15, 9, 7, 3, 1, ";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testCodeContains1()
    {
        boolean passed = checkCodeContains("correct starting index", "int i = a1.length-1;");
        assertTrue(passed);
    }

@Test
    public void testCodeContains2()
    {
        boolean passed = checkCodeContains("correct ending index", "i >= 0;");
        assertTrue(passed);
    }

@Test
    public void testCodeContains3()
    {
        boolean passed =
                checkCodeContains(
                        "correct array variable name", "System.out.print(a1[i] + \", \");");
        assertTrue(passed);
    }
}

Activity 4.20.3.

Rewrite the following code so that it prints all the values in an array arr1 using a for-each loop instead of a for loop.

Activity 4.20.4.

Finish the following code so that it prints out all of the odd values in the array a1. Hint: use % to check for odd values.

Activity 4.20.5.

Finish the following method getSum to return the sum of all values in the passed array.

public class Test1
{

public static int getSum(int[] arr)
    {

}

public static void main(String[] args)
    {
        int[] a1 = {1, 2, 5, 3};
        System.out.println(
                "It should print 11 " + " and your answer is: " + getSum(a1));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "It should print 11  and your answer is: 11";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testMethod()
    {
        int[] nums = {10, 20, 30, 40, 50};
        Object[] args = {nums};

// name of method, arguments are (nums, 30)
        String output = getMethodOutput("getSum", args);
        String expect = "150";

boolean passed = getResults(expect, output, "getSum({10, 20, 30, 40, 50})");
        assertTrue(passed);
    }
}

Activity 4.20.6.

Finish the following method to return the sum of all of the non-negative values in the passed array.

public class Test1
{

public static int getSumNonNeg(int[] arr)
    {

}

public static void main(String[] args)
    {
        int[] a1 = {1, 2, 5, 3, -1, -20};
        System.out.println(
                "The code should print 11 "
                        + "and your answer is: "
                        + getSumNonNeg(a1));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "The code should print 11 and your answer is: 11";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testMethod()
    {
        int[] nums = {10, -20, 30, -40, 50};
        Object[] args = {nums};

// name of method, arguments are (nums, 30)
        String output = getMethodOutput("getSumNonNeg", args);
        String expect = "90";

boolean passed = getResults(expect, output, "getSum({10, -20, 30, -40, 50})");
        assertTrue(passed);
    }
}

Activity 4.20.7.

Finish the following code to print the strings at the odd indices in the array.

Activity 4.20.8.

Finish the method getSumChars below to return the total number of characters in the array of strings strArr.

public class Test1
{

public static int getSumChars(String[] strArr)
    {

}

public static void main(String[] args)
    {
        String[] strArr = {"hi", "bye", "hola"};
        System.out.println(getSumChars(strArr));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "9";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testCodeContains1()
    {
        boolean passed = checkCodeContains("adding length of each string", ".length()");
        assertTrue(passed);
    }

@Test
    public void testCodecontains()
    {
        boolean passed = checkCodeContains("for loop", "for");
        assertTrue(passed);
    }

@Test
    public void testMethod()
    {
        String[] strs = {"a", "aa", "aaa"};
        Object[] args = {strs};

// name of method, arguments are (nums, 30)
        String output = getMethodOutput("getSumChars", args);
        String expect = "6";

boolean passed = getResults(expect, output, "getSumChars({\"a\",\"aa\",\"aaa\"})");
        assertTrue(passed);
    }
}

Activity 4.20.9.

Finish the method findMin so that it finds and returns the minimum value in the array.

public class Test1
{

public static int findMin(int[] arr)
    {

}

public static void main(String[] args)
    {
        int[] arr = {20, -3, 18, 55, 4};
        System.out.println(findMin(arr));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "-3";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testCodeContains2()
    {
        boolean passed = checkCodeContains("for loop", "for");
        assertTrue(passed);
    }

@Test
    public void testMethod()
    {
        int[] nums = {10, 20, 5, 40, 60};
        Object[] args = {nums};
        String output = getMethodOutput("findMin", args);
        String expect = "5";

boolean passed = (output.equals(expect));
        getResults(expect, output, "findMin({10, 20, 5, 40, 60})", passed);
        assertTrue(passed);
    }
}

Activity 4.20.10.

Finish the method getAverage to calculate and return the average of all of the values in the array.

public class Test1
{

public static double getAverage(int[] arr)
    {

}

public static void main(String[] args)
    {
        int[] arr = {20, 3, 18, 55, 4};
        System.out.println(getAverage(arr));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "20.0";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testCodeContains2()
    {
        boolean passed = checkCodeContains("for loop", "for");
        assertTrue(passed);
    }

@Test
    public void testMethod()
    {
        int[] nums = {10, 20, 30, 40, 50};
        Object[] args = {nums};

// name of method, arguments are (nums, 30)
        String output = getMethodOutput("getAverage", args);
        String expect = "30.0";

boolean passed = getResults(expect, output, "getAverage({10, 20, 30, 40, 50})");
        assertTrue(passed);
    }
}

Section 4.20 Arrays Code Practice

Subsection 4.20.1 Practice Problems

Activity 4.20.1.

Activity 4.20.2.

Activity 4.20.3.

Activity 4.20.4.

Activity 4.20.5.

Activity 4.20.6.

Activity 4.20.7.

Activity 4.20.8.

Activity 4.20.9.

Activity 4.20.10.

Subsection 4.20.2 More Practice