completing missing Exercises

.gitignore

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+/.idea/
+/out/
+/java-prog-dan-lang-10th.iml

src/ch_02/Ex0215.java

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+package ch_02;
+import java.util.Scanner;
+/*
+ 2.15 (Geometry: distance of two points) Write a program that prompts the user to enter
+two points (x1, y1) and (x2, y2) and displays their distance between them.
+The formula for computing the distance is sqrt[(x2 - x1)^2 + (y2 - y1)^2)]. Note that
+you can use Math.pow(a, 0.5) to compute sqrt(a). Sample run:
+
+Enter x1 and y1: 1.5 -3.4
+Enter x2 and y2: 4 5
+The distance between the two points is 8.764131445842194
+*/
+
+
+public class Ex0215 {
+
+  public static void main(String[] args){
+      Scanner input = new Scanner(System.in);
+      System.out.println("Enter x1 and y1: ");
+      double x1, x2, y1, y2;
+
+      x1 = input.nextDouble();
+      y1 = input.nextDouble();
+
+      System.out.println("Enter x2 and y2: ");
+
+      x2 = input.nextDouble();
+      y2 = input.nextDouble();
+
+      double exs = Math.pow((x2 - x1),2);
+      double whys = Math.pow((y2 - y1),2);
+
+      double a = Math.pow((exs + whys),0.5);
+
+      System.out.println("The distance between the two points is " + a);
+
+
+  }
+
+}

src/ch_02/Ex0216.java

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+package ch_02;
+/*
+2.16 (Geometry: area of a hexagon) Write a program that prompts the user to enter the
+side of a hexagon and displays its area.
+*/
+
+import java.util.Scanner;
+
+
+public class Ex0216 {
+    public static void main(String[] args) {
+        Scanner input = new Scanner(System.in);
+
+        System.out.println("Enter a decimal for the length of the side of a hexagon: ");
+        double side = input.nextDouble();
+
+        double operand = (3 * Math.pow(3, 0.5)) / 2;
+        double res = operand * Math.pow(side, 2);
+        System.out.println("The area of the hexagon is " + res);
+
+    }
+}

src/ch_02/Ex0217.java

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+package ch_02;
+
+import java.util.Scanner;
+/*
+*2.17 (Science: wind-chill temperature) How cold is it outside? The temperature alone
+is not enough to provide the answer. Other factors including wind speed, relative
+humidity, and sunshine play important roles in determining coldness outside.
+In 2001, the National Weather Service (NWS) implemented the new wind-chill
+temperature to measure the coldness using temperature and wind speed. The
+formula is
+twc = 35.74 + 0.6215ta - 35.75v0.16 + 0.4275tav0.16
+where ta is the outside temperature measured in degrees Fahrenheit and v is the
+speed measured in miles per hour. twc is the wind-chill temperature. The formula
+cannot be used for wind speeds below 2 mph or temperatures below -58 ºF or
+above 41ºF.
+Write a program that prompts the user to enter a temperature between -58 ºF and
+41ºF and a wind speed greater than or equal to 2 and displays the wind-chill
+*/
+
+public class Ex0217 {
+  public static void main(String[] args){
+    Scanner input = new Scanner(System.in);
+
+    System.out.println("Enter the temperature in Fahrenheit between -58°F and 41°F: ");
+    double temp = input.nextDouble();
+
+    System.out.println("Enter the wind speed (>=2) in miles per hour: ");
+    int windSpeed = input.nextInt();
+
+    double vToPow16 = Math.pow(windSpeed,0.16);
+
+    double twc = 35.74 + 0.6215 * temp - 35.75 * vToPow16 + 0.4275 * temp * vToPow16;
+    System.out.println("The wind chill index is " + twc);
+
+    }
+
+
+}

src/ch_02/Ex0218.java

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+package ch_02;
+
+/*
+2.18 (Print a table) Write a program that displays the following table. Cast floating point
+numbers into integers.
+a b pow(a, b)
+1 2 1
+2 3 8
+3 4 81
+4 5 1024
+5 6 15625
+*/
+
+public class Ex0218 {
+  public static void main(String[] args){
+    System.out.println("a    b    pow(a,b)");
+    int a,b;
+    a = 1; b =2;
+    System.out.println(a + "    "  +  b +  "    " + (int)Math.pow(a,b));
+    a++; b++;
+    System.out.println(a + "    "  +  b +  "    " + (int)Math.pow(a,b));
+    a++; b++;
+    System.out.println(a + "    "  +  b +  "    " + (int)Math.pow(a,b));
+    a++; b++;
+    System.out.println(a + "    "  +  b +  "    " + (int)Math.pow(a,b));
+    a++; b++;
+    System.out.println(a + "    "  +  b +  "    " + (int)Math.pow(a,b));
+  }
+}

src/ch_02/Ex0220.java

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+package ch_02;
+
+import java.util.Scanner;
+
+/*
+*2.20 (Financial application: calculate interest) If you know the balance and the annual
+percentage interest rate, you can compute the interest on the next monthly payment
+using the following formula:
+interest = balance * (annualInterestRate/1200)
+Write a program that reads the balance and the annual percentage interest rate and
+displays the interest for the next month.
+* Example:
+* Enter balance and interest rate (e.g., 3 for 3%): 1000 3.5
+The interest is 2.91667
+ */
+public class Ex0220 {
+    public static void main(String[] args) {
+        Scanner input = new Scanner(System.in);
+        System.out.println("Enter balance and interest rate: (e.g., 3 for 3%): ");
+
+        double balance = input.nextDouble();
+        double rate = input.nextDouble();
+        double interest = balance * (rate/1200);
+        double roundedInterest = Math.round(interest * 100000)/100000.0;
+        System.out.println("The interest rate is: " + roundedInterest);
+
+
+
+
+    }
+}

src/ch_02/Exercise0209.java

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+package ch_02;
+
+import java.util.Scanner;
+
+/*2.9 (Physics: acceleration) Average acceleration is defined as the change of velocity
+divided by the time taken to make the change, as shown in the following formula:
+a =
+v1 - v0
+t
+Write a program that prompts the user to enter the starting velocity v0 in meters/
+second, the ending velocity v1 in meters/second, and the time span t in seconds,
+and displays the average acceleration. Here is a sample run:
+*/
+
+public class Exercise0209 {
+
+  public static void main(String[] args) {
+    Scanner input = new Scanner(System.in);
+
+    System.out.println("Enter v0, v1, and t:  ");
+    double v0,v1,t;
+
+    v0 = input.nextDouble();
+    v1 = input.nextDouble();
+    t = input.nextDouble();
+
+    double a = (v1 - v0) / t;
+
+    System.out.println("Acceleration is " + a);
+
+
+  }
+
+
+}

src/ch_02/Exercise0211.java

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+package ch_02;
+
+/*
+2.11 (Population projection) Rewrite Programming Exercise 1.11 to prompt the user
+to enter the number of years and displays the population after the number of years.
+Use the hint in Programming Exercise 1.11 for this program. The population
+should be cast into an integer.
+*/
+
+import java.util.Scanner;
+
+public class Exercise0211 {
+    public static void main(String[] args) {
+        Scanner input = new Scanner(System.in);
+        System.out.println("Enter the number of years: ");
+        int numYears = input.nextInt();
+
+        int currentPopulation = 312_032_486;
+        double daysInYear = 365.00;
+        double secInYear = daysInYear * 24 * 60 * 60;
+        double birthsPerYear = 7 / 60.0 * secInYear;
+        System.out.println(birthsPerYear);
+        double deathsPerYear = 13 / 60.0 * secInYear;
+        double imigrationPerYear = 45 / 60.0 * secInYear;
+        System.out.println(deathsPerYear);
+        System.out.println(imigrationPerYear);
+
+        double changePerYear = imigrationPerYear + birthsPerYear - deathsPerYear;
+        double totalPopAfterYears = changePerYear * numYears;
+        int result = (int) (totalPopAfterYears + currentPopulation);
+        System.out.println("The population in " + numYears + " years will be " + result);
+        System.out.println("Since the change per year is " + (int)(changePerYear));
+    }
+}

src/ch_02/Exercise0212.java

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+package ch_02;
+
+import java.util.Scanner;
+
+/*
+(Physics: finding runway length) Given an airplane’s acceleration a and take-off
+speed v, you can compute the minimum runway length needed for an airplane to
+take off using the following formula:
+length =v^2 / 2*a
+Write a program that prompts the user to enter v in meters/second (m/s) and the
+acceleration a in meters/second squared (m/s2), and displays the minimum runway
+length.
+*/
+public class Exercise0212 {
+    public static void main(String[] args) {
+        Scanner input = new Scanner(System.in);
+
+        System.out.println("Enter speed and acceleration: ");
+        int v = input.nextInt();
+        double acc = input.nextDouble();
+
+        double numerator = Math.pow(v, 2);
+        double denominator = 2 * acc;
+        double minRunwayLength = numerator / denominator;
+        System.out.println("The minimum runway length for this airplane is "
+                + minRunwayLength);
+
+
+    }
+}