diff --git a/ch03/Convert.java b/ch02/Convert.java
similarity index 100%
rename from ch03/Convert.java
rename to ch02/Convert.java
diff --git a/ch02/Date.java b/ch02/Date.java
new file mode 100644
index 0000000..85b0395
--- /dev/null
+++ b/ch02/Date.java
@@ -0,0 +1,12 @@
+
+public class Date {
+    public static void main(String [] args) {
+        String day = "Monday, ";
+        int date = 1;
+        String month = "March ";
+        int year = 2026;
+
+        System.out.println("American format: " + day + month + date + ", " + year);
+        System.out.println("European format: " + day + date + " " + month + year);
+    }
+}
diff --git a/ch02/DeclareAssign.java b/ch02/DeclareAssign.java
index 87a8e02..e701d68 100644
--- a/ch02/DeclareAssign.java
+++ b/ch02/DeclareAssign.java
@@ -12,7 +12,7 @@ public static void main(String[] args) {
         hour = 11;           // assign the value 11 to hour
         minute = 59;         // set minute to 59
 
-        message = "123";     // legal
+        message = "123";        // legal
         // message = 123;    // not legal
 
         String message2 = "Hello!";
diff --git a/ch03/Echo.java b/ch02/Echo.java
similarity index 100%
rename from ch03/Echo.java
rename to ch02/Echo.java
diff --git a/ch02/FloatingPoint.java b/ch02/FloatingPoint.java
index b9afa1c..3ce28c3 100644
--- a/ch02/FloatingPoint.java
+++ b/ch02/FloatingPoint.java
@@ -4,10 +4,6 @@ public static void main(String[] args) {
         double pi;
         pi = 3.14159;
 
-        double minute3 = 59.0;
-        System.out.print("Fraction of the hour that has passed: ");
-        System.out.println(minute3 / 60.0);
-
         double y = 1.0 / 3.0;  // correct
 
         System.out.println(0.1 * 10);
diff --git a/ch03/Formatting.java b/ch02/Formatting.java
similarity index 100%
rename from ch03/Formatting.java
rename to ch02/Formatting.java
diff --git a/ch03/Literals.java b/ch02/Literals.java
similarity index 100%
rename from ch03/Literals.java
rename to ch02/Literals.java
diff --git a/ch02/PrintingVars.java b/ch02/PrintingVars.java
index 27a0f08..ed7cb0c 100644
--- a/ch02/PrintingVars.java
+++ b/ch02/PrintingVars.java
@@ -19,7 +19,7 @@ public static void main(String[] args) {
         System.out.println(hour * 60 + minute);
 
         System.out.print("Fraction of the hour that has passed: ");
-        System.out.println(minute / 60);
+        System.out.println(hour * 60);
 
         System.out.print("Percent of the hour that has passed: ");
         System.out.println(minute * 100 / 60);
diff --git a/ch03/ScannerBug.java b/ch02/ScannerBug.java
similarity index 100%
rename from ch03/ScannerBug.java
rename to ch02/ScannerBug.java
diff --git a/ch02/Time.java b/ch02/Time.java
new file mode 100644
index 0000000..68b1301
--- /dev/null
+++ b/ch02/Time.java
@@ -0,0 +1,16 @@
+public class Time {
+    public static void main(String[] args) {
+        int hour = 22;
+        int minute = 44;
+        int second = 59;
+
+        int secondsSinceMidNight = (22 * 60 * 60) + 59;
+        System.out.println(secondsSinceMidNight);
+
+        int secondsRemaining = (24 * 60 * 60) - secondsSinceMidNight;
+        System.out.println(secondsRemaining);
+
+        double percentagePast = (secondsSinceMidNight * 100.0) / (24.0 * 60.0 * 60.0);
+        System.out.println(percentagePast);
+    }
+}
diff --git a/ch03/GuessStarter.java b/ch03/GuessStarter.java
index 64984df..df0fd85 100644
--- a/ch03/GuessStarter.java
+++ b/ch03/GuessStarter.java
@@ -1,4 +1,5 @@
 import java.util.Random;
+import java.util.Scanner;
 
 /**
  * Starter code for the "Guess My Number" exercise.
@@ -9,7 +10,18 @@ public static void main(String[] args) {
         // pick a random number
         Random random = new Random();
         int number = random.nextInt(100) + 1;
-        System.out.println(number);
+        int userGuess;
+
+        System.out.println("I'm thinking of a number between 1 and 100");
+        System.out.println("(including both). Can you guess what it is?");
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Type a number ");
+        userGuess = scanner.nextInt();
+
+        System.out.println("Your guess is: " + userGuess);
+        System.out.println("The number I was thinking of is: " + number);
+        System.out.println("You were off by: " + (number - userGuess));
     }
 
 }
diff --git a/ch03/SecondsConverter.java b/ch03/SecondsConverter.java
new file mode 100644
index 0000000..ec613cb
--- /dev/null
+++ b/ch03/SecondsConverter.java
@@ -0,0 +1,21 @@
+import java.util.Scanner;
+
+public class SecondsConverter {
+    public static void main(String[] args) {
+        int hours;
+        int minutes;
+        int seconds;
+        final int Seconds_In_Hour = 3600;
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter how many seconds you want to calculate: ");
+        seconds = scanner.nextInt();
+        scanner.close();
+
+        hours = seconds / Seconds_In_Hour;
+        minutes = (seconds % Seconds_In_Hour) / 60;
+        seconds = seconds % 60;
+
+        System.out.printf("%d hours, %d minutes, %d seconds\n", hours, minutes, seconds);
+    }
+}
diff --git a/ch03/TempConverter.java b/ch03/TempConverter.java
new file mode 100644
index 0000000..a82a12c
--- /dev/null
+++ b/ch03/TempConverter.java
@@ -0,0 +1,14 @@
+import java.util.Scanner;
+
+public class TempConverter {
+    public static void main(String[] args) {
+        double celsius;
+        Scanner userInput = new Scanner(System.in);
+
+        System.out.print("Enter a temperature in Celsius: ");
+        celsius = userInput.nextDouble();
+        double Fahrenheit = (celsius * 9/5) + 32;
+
+        System.out.printf("%.1f C = %.2f F\n", celsius, Fahrenheit);
+    }
+}
diff --git a/ch04/DateFromSecondChapter_4_1.java b/ch04/DateFromSecondChapter_4_1.java
new file mode 100644
index 0000000..0dd4f1d
--- /dev/null
+++ b/ch04/DateFromSecondChapter_4_1.java
@@ -0,0 +1,19 @@
+public class DateFromSecondChapter_4_1 {
+    public static void printAmerican(String day, int date, String month, int year) {
+        System.out.println("American format: " + day + ", " + month + " " + date + ", " + year);
+    }
+
+    public static void printEuropean(String day, int date, String month, int year) {
+        System.out.println("European format: " + day + " " + date + ", " + month + " " + year);
+    }
+
+    public static void main(String [] args) {
+        String day = "Monday";
+        int date = 9;
+        String month = "March";
+        int year = 2026;
+
+        printAmerican(day, date, month, year);
+        printEuropean(day, date, month, year);
+    }
+}
diff --git a/ch04/Multadd.java b/ch04/Multadd.java
new file mode 100644
index 0000000..7598448
--- /dev/null
+++ b/ch04/Multadd.java
@@ -0,0 +1,22 @@
+public class Multadd {
+    public static double multadd(double a, double b, double c) {
+        return a * b + c;
+    }
+
+    public static double expSum(double x) {
+        return multadd(x, Math.exp(-x), Math.sqrt(1 - Math.exp(-x)));
+    }
+
+    public static void main(String[] args) {
+        System.out.println(multadd(1.0, 2.0, 3.0));
+
+        double val1 = multadd(Math.sin(Math.PI / 4), 1.0, Math.cos(Math.PI / 4) / 2);
+        System.out.println(val1);
+
+        double val2 = multadd(1.0, Math.log(10), Math.log(20));
+        System.out.println(val2);
+
+        System.out.println(expSum(1.0));
+        System.out.println(expSum(2.0));
+    }
+}
diff --git a/ch04/PrintTwice.java b/ch04/PrintTwice.java
index 1180417..2515cfb 100644
--- a/ch04/PrintTwice.java
+++ b/ch04/PrintTwice.java
@@ -1,3 +1,4 @@
+
 public class PrintTwice {
 
     public static void printTwice(String s) {
diff --git a/ch05/Ex_5_1.java b/ch05/Ex_5_1.java
new file mode 100644
index 0000000..9890c15
--- /dev/null
+++ b/ch05/Ex_5_1.java
@@ -0,0 +1,12 @@
+import java.util.Scanner;
+
+public class Ex_5_1 {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        int x = in.nextInt();
+
+        if (x > 0 && x < 10) {
+            System.out.println("positive single digit number");
+        }
+    }
+}
\ No newline at end of file
diff --git a/ch05/Ex_5_2.java b/ch05/Ex_5_2.java
new file mode 100644
index 0000000..db9e32c
--- /dev/null
+++ b/ch05/Ex_5_2.java
@@ -0,0 +1,37 @@
+import java.util.Random;
+import java.util.Scanner;
+
+public class Ex_5_2 {
+    public static void main(String[] args) {
+        Random random = new Random();
+        int number = random.nextInt(100) + 1;
+        int userGuess;
+        int userAttempts = 3;
+
+        System.out.println("I'm thinking of a number between 1 and 100");
+        System.out.println("(including both). Can you guess what it is?");
+
+        Scanner scanner = new Scanner(System.in);
+
+        while(userAttempts != 0 ) {
+            System.out.print("Type a number ");
+            userGuess = scanner.nextInt();
+
+            if (userGuess < number) {
+                System.out.println("Your number is less than the number I'm thinking about");
+                userAttempts--;
+            } else if (userGuess > number) {
+                System.out.println("Your number is bigger than the number I'm thinking about");
+                userAttempts--;
+            } else {
+                System.out.println("Congratulations! You guessed right!");
+                break;
+            }
+
+            if (userAttempts == 0) {
+                System.out.println("I'm sorry you are out of attempts");
+                System.out.println("The number I was thinking of is: " + number);
+            }
+        }
+    }
+}
diff --git a/ch05/Fermat.java b/ch05/Fermat.java
new file mode 100644
index 0000000..032eee0
--- /dev/null
+++ b/ch05/Fermat.java
@@ -0,0 +1,28 @@
+import java.util.Scanner;
+
+public class Fermat {
+    public static void main(String[] args) {
+        int a;
+        int b;
+        int c;
+        int n;
+
+        Scanner in = new Scanner(System.in);
+        System.out.print("What's your 'a' number? ");
+        a = in.nextInt();
+        System.out.print("What's your 'b' number? ");
+        b = in.nextInt();
+        System.out.print("What's your 'c' number? ");
+        c = in.nextInt();
+        System.out.print("What's your 'n' number? ");
+        n = in.nextInt();
+
+        boolean result = Math.pow(a, n) + Math.pow(b, n) == Math.pow(c, n);
+
+        if (n > 2 && result) {
+            System.out.println("Holy smokes, Fermat was wrong!");
+        } else {
+            System.out.println("No, that doesn't work.");
+        }
+    }
+}
diff --git a/ch05/Quadratic.java b/ch05/Quadratic.java
new file mode 100644
index 0000000..beb93ef
--- /dev/null
+++ b/ch05/Quadratic.java
@@ -0,0 +1,45 @@
+import java.util.Scanner;
+
+public class Quadratic {
+    public static void main(String[] args) {
+        int a;
+        int b;
+        int c;
+
+        Scanner in = new Scanner(System.in);
+
+        System.out.print("Enter a number ");
+        if (!in.hasNextInt()) {
+            System.out.println("Error: \"" + in.next() + "\" is not a valid integer.");
+            return;
+        }
+        a = in.nextInt();
+
+        System.out.print("Enter a number ");
+        if (!in.hasNextInt()) {
+            System.out.println("Error: \"" + in.next() + "\" is not a valid integer.");
+            return;
+        }
+        b = in.nextInt();
+
+        System.out.print("Enter a number ");
+        if (!in.hasNextInt()) {
+            System.out.println("Error: \"" + in.next() + "\" is not a valid integer.");
+            return;
+        }
+        c = in.nextInt();
+
+        double discriminant = b * b - 4 * a * c;
+
+        if (a == 0) {
+            System.out.println("The value of 'a' cannot be zero.");
+        } else if (discriminant < 0) {
+            System.out.println("No real solutions.");
+        } else {
+            double x1 = (-b + Math.sqrt(discriminant)) / (2 * a);
+            double x2 = (-b - Math.sqrt(discriminant)) / (2 * a);
+            System.out.println("x1 = " + x1);
+            System.out.println("x2 = " + x2);
+        }
+    }
+}
diff --git a/ch05/Triangle.java b/ch05/Triangle.java
new file mode 100644
index 0000000..7c8fd1f
--- /dev/null
+++ b/ch05/Triangle.java
@@ -0,0 +1,45 @@
+import java.util.Scanner;
+
+public class Triangle {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        System.out.print("Enter a number ");
+        if (!in.hasNextInt()) {
+            System.out.println("Error: \"" + in.next() + "\" is not a valid integer.");
+            return;
+        }
+        int a = in.nextInt();
+        if (a <= 0) {
+            System.err.println("Error: " + a + " is less than or equal to 0.");
+            return;
+        }
+
+        System.out.print("Enter a number ");
+        if (!in.hasNextInt()) {
+            System.out.println("Error: \"" + in.next() + "\" is not a valid integer.");
+            return;
+        }
+        int b = in.nextInt();
+        if (b <= 0) {
+            System.err.println("Error: " + b + " is less than or equal to 0.");
+            return;
+        }
+
+        System.out.print("Enter a number ");
+        if (!in.hasNextInt()) {
+            System.out.println("Error: \"" + in.next() + "\" is not a valid integer.");
+            return;
+        }
+        int c = in.nextInt();
+        if (c <= 0) {
+            System.err.println("Error: " + c + " is less than or equal to 0.");
+            return;
+        }
+
+        if (a + b > c && a + c > b && b + c > a) {
+            System.out.println("Yes, these sides can form a triangle.");
+        } else {
+            System.out.println("No, these sides cannot form a triangle.");
+        }
+    }
+}
diff --git a/ch06/Ex_6_2_SquareRoot.java b/ch06/Ex_6_2_SquareRoot.java
new file mode 100644
index 0000000..f77a458
--- /dev/null
+++ b/ch06/Ex_6_2_SquareRoot.java
@@ -0,0 +1,21 @@
+public class Ex_6_2_SquareRoot {
+    public static void main(String[] a) {
+        System.out.println(squareRoot(9));    // should be ~3.0
+        System.out.println(squareRoot(25));   // should be ~5.0
+        System.out.println(squareRoot(2));    // should be ~1.4142
+    }
+
+    public static double squareRoot(double a) {
+        double x = a /2;
+
+        while (true) {
+            double next = (x + a / x) / 2;
+
+            if (Math.abs(next - x) < 0.0001) {
+                return next;
+            }
+
+            x = next;
+        }
+    }
+}
diff --git a/ch06/isDoubloon.java b/ch06/isDoubloon.java
new file mode 100644
index 0000000..a8e013a
--- /dev/null
+++ b/ch06/isDoubloon.java
@@ -0,0 +1,27 @@
+public class isDoubloon {
+    public static boolean doubloon(String s) {
+        String lower = s.toLowerCase();
+        int[] counts = new int[26];
+
+        for (int i = 0; i < s.length(); i++) {
+            char letter = lower.charAt(i);
+            int index = letter - 'a';
+            counts[index]++;
+        }
+
+        for (int count:counts) {
+            if (count != 0 && count != 2) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(doubloon("beriberi"));
+        System.out.println(doubloon("boob"));
+        System.out.println(doubloon("tit"));
+        System.out.println(doubloon("Caucasus"));
+    }
+}
diff --git a/ch07/Fruit.java b/ch07/Fruit.java
index 50428c5..8a32c4a 100644
--- a/ch07/Fruit.java
+++ b/ch07/Fruit.java
@@ -3,9 +3,10 @@
  */
 public class Fruit {
 
+    // Multiplication of all elements
     public static int banana(int[] a) {
-        int kiwi = 1;
-        int i = 0;
+        int kiwi = 1; // counter
+        int i = 0; // beginner
         while (i < a.length) {
             kiwi = kiwi * a[i];
             i++;
@@ -13,6 +14,7 @@ public static int banana(int[] a) {
         return kiwi;
     }
 
+    // Looking for the number in the array;
     public static int grapefruit(int[] a, int grape) {
         for (int i = 0; i < a.length; i++) {
             if (a[i] == grape) {
@@ -22,6 +24,7 @@ public static int grapefruit(int[] a, int grape) {
         return -1;
     }
 
+    // Counting how many number appears in the array that we are looking for;
     public static int pineapple(int[] a, int apple) {
         int pear = 0;
         for (int pine: a) {
@@ -31,5 +34,4 @@ public static int pineapple(int[] a, int apple) {
         }
         return pear;
     }
-
 }
diff --git a/ch07/MakeDubMus.java b/ch07/MakeDubMus.java
index 9c7e193..69023d8 100644
--- a/ch07/MakeDubMus.java
+++ b/ch07/MakeDubMus.java
@@ -11,12 +11,14 @@ public static int[] make(int n) {
         return a;
     }
 
+    // Multiplies each number to 2;
     public static void dub(int[] jub) {
         for (int i = 0; i < jub.length; i++) {
-            jub[i] *= 2;
+            jub[i] *= 2; //
         }
     }
 
+    // Addition of the array zoo;
     public static int mus(int[] zoo) {
         int fus = 0;
         for (int i = 0; i < zoo.length; i++) {
@@ -26,9 +28,9 @@ public static int mus(int[] zoo) {
     }
 
     public static void main(String[] args) {
-        int[] bob = make(5);
-        dub(bob);
-        System.out.println(mus(bob));
+        int[] bob = make(5); // [1, 2, 3, 4, 5]
+        dub(bob); // [2, 4, 8, 16, 32]
+        System.out.println(mus(bob)); //
     }
 
 }
diff --git a/ch07/indexOfMax.java b/ch07/indexOfMax.java
new file mode 100644
index 0000000..cd24b9c
--- /dev/null
+++ b/ch07/indexOfMax.java
@@ -0,0 +1,21 @@
+public class indexOfMax {
+    public static int indexOfMaxMethod(int[] numbers) {
+        int result = 0;
+        int maxVal = numbers[0];
+
+        for (int i = 1; i < numbers.length; i++) {
+            if (numbers[i] > maxVal) {
+                maxVal = numbers[i];
+                result = i;
+            }
+        }
+
+        return result;
+    }
+
+    public static void main(String[] args) {
+        int[] test = {3, 7, 1, 9, 12};
+
+        System.out.println(indexOfMaxMethod(test));
+    }
+}