ch 18

Author: HarryDulaney

src/ch_18/Exercise18_10.java

@@ -27,10 +27,13 @@ public static void main(String[] args) {
 
     public static int count(String str, char a) {
         if (str.length() > 0) {
-            count += str.charAt(str.length() - 1) == a ? 1 : 0;
-            count(str.substring(0, str.length() - 1), a);
+            if (str.charAt(str.length() - 1) == a) {
+                return 1 + count(str.substring(0, str.length() - 1), a);
+            } else {
+                return count(str.substring(0, str.length() - 1), a);
+            }
         }
-        return count;
+        return 0;
 
     }
 }

src/ch_18/Exercise18_13.java

@@ -0,0 +1,34 @@
+package ch_18;
+
+import java.util.Scanner;
+
+/**
+ * *18.13 (Find the largest number in an array) Write a recursive method that returns the
+ * largest integer in an array.
+ * <p>
+ * Write a test program that prompts the user to enter a list of eight integers and displays the largest element.
+ */
+public class Exercise18_13 {
+    static int currIdx = 0;
+
+    public static void main(String[] args) {
+        int[] arr = new int[8];
+        Scanner in = new Scanner(System.in);
+        System.out.println("Enter a list of eight integers: ");
+        for (int i = 0; i < 8; i++) {
+            arr[i] = in.nextInt();
+        }
+        in.close();
+        System.out.println("The largest integer in the list is " + largestInteger(Integer.MIN_VALUE, arr));
+
+
+    }
+
+    static int largestInteger(int large, int[] integers) {
+        if (currIdx == integers.length) {
+            return large;
+        }
+        large = Math.max(large, integers[currIdx++]);
+        return largestInteger(large, integers);
+    }
+}

src/ch_18/Exercise18_14.java

@@ -0,0 +1,30 @@
+package ch_18;
+
+import java.util.Scanner;
+
+/**
+ * *18.14 (Find the number of uppercase letters in a string)
+ * Write a recursive method to return the number of uppercase letters in a string.
+ * <p>
+ * Write a test program that prompts the user to enter a string and displays the number of uppercase letters in
+ * the string.
+ */
+public class Exercise18_14 {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        System.out.print("Enter a String: ");
+        String s = in.nextLine().trim();
+        System.out.println("The number of uppercase letters in " + s + " is: " + numUpperCase(s, 0, 0));
+
+    }
+
+    static int numUpperCase(String str, int idx, int count) {
+        if (idx == str.length()) {
+            return count;
+        }
+        if (Character.isUpperCase(str.charAt(idx))) {
+            count++;
+        }
+        return numUpperCase(str, ++idx, count);
+    }
+}

src/ch_18/Exercise18_15.java

@@ -0,0 +1,33 @@
+package ch_18;
+
+import java.util.Scanner;
+
+/**
+ * *18.15 (Occurrences of a specified character in a string) Rewrite Programming Exercise 18.10 using a helper
+ * method to pass the substring high index to the method.
+ * The helper method header is:
+ * public static int count(String str, char a, int high)
+ */
+public class Exercise18_15 {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        System.out.print("Enter a String and a character to count it's occurrences:");
+        String str = in.next();
+        char ch = in.next().charAt(0);
+
+        System.out.println("Character " + ch + " occurs " + count(str, ch) + " times in " + str);
+        in.close();
+    }
+
+    public static int count(String str, char a, int high) {
+        if (high > 0) {
+            return str.charAt(high) == a ? (1 + count(str, a, high - 1)) : (count(str, a, high - 1));
+        } else {
+            return 0;
+        }
+    }
+
+    public static int count(String str, char a) {
+        return count(str, a, str.length() - 1);
+    }
+}

src/ch_18/Exercise18_16.java

@@ -0,0 +1,38 @@
+package ch_18;
+
+import java.util.Scanner;
+
+/**
+ * *18.16 (Find the number of uppercase letters in an array) Write a recursive method
+ * to return the number of uppercase letters in an array of characters. You need to
+ * define the following two methods. The second one is a recursive helper method.
+ * public static int count(char[] chars)
+ * public static int count(char[] chars, int high)
+ * Write a test program that prompts the user to enter a list of characters in one line
+ * and displays the number of uppercase letters in the list.
+ */
+public class Exercise18_16 {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        System.out.print("Enter a list of characters in one line: ");
+
+        String line = in.nextLine();
+        char[] chars = line.toCharArray();
+
+        System.out.println("The number of uppercase letters in the list is: " + count(chars));
+        in.close();
+    }
+
+    public static int count(char[] chars) {
+        return count(chars, chars.length - 1);
+    }
+
+    public static int count(char[] chars, int high) {
+        if (high > 0) {
+            return Character.isUpperCase(chars[high]) ? (1 + count(chars, high - 1)) : (count(chars, high - 1));
+        } else {
+            return 0;
+        }
+
+    }
+}

src/ch_18/Exercise18_17.java

@@ -0,0 +1,38 @@
+package ch_18;
+
+import java.util.Scanner;
+
+/**
+ * *18.17 (Occurrences of a specified character in an array) Write a recursive method that
+ * finds the number of occurrences of a specified character in an array. You need to
+ * define the following two methods. The second one is a recursive helper method.
+ * public static int count(char[] chars, char ch)
+ * public static int count(char[] chars, char ch, int high)
+ * Write a test program that prompts the user to enter a list of characters in one line,
+ * and a character, and displays the number of occurrences of the character in the list.
+ */
+public class Exercise18_17 {
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        System.out.print("Enter a list of characters in one line: ");
+        String line = in.nextLine();
+        char[] chars = line.toCharArray();
+
+        System.out.println("Enter a single character: ");
+        char ch = in.next().charAt(0);
+        System.out.println("The character " + ch + " occurs " + count(chars, ch) + " times.");
+        in.close();
+    }
+
+    public static int count(char[] chars, char ch) {
+        return count(chars, ch, chars.length - 1);
+    }
+
+    public static int count(char[] chars, char ch, int high) {
+        if (high > 0) {
+            return chars[high] == ch ? (1 + count(chars, ch, high - 1)) : (count(chars, ch, high - 1));
+        } else {
+            return 0;
+        }
+    }
+}