bits and english alphabet

Author: ZapDos7

README.md

@@ -56,7 +56,9 @@
 - [x] [Bit Hacks — Part 1 (Basic)](http://www.techiedelight.com/bit-hacks-part-1-basic/)
 - [x] [Bit Hacks — Part 2 (Playing with k’th bit)](http://www.techiedelight.com/bit-hacks-part-2-playing-kth-bit/)
 - [x] [Bit Hacks — Part 3 (Playing with rightmost set bit of a number)](http://www.techiedelight.com/bit-hacks-part-3-playing-rightmost-set-bit-number/)
-
+- [x] [Bit Hacks — Part 4 (Playing with letters of English alphabet)](http://www.techiedelight.com/bit-hacks-part-4-playing-letters-english-alphabet/)
+- [ ] [Bit Hacks — Part 5 (Find absolute value of an integer without branching)](http://www.techiedelight.com/bit-hacks-part-5-find-absolute-value-integer-without-branching/)
+- [ ] [Bit Hacks — Part 6 (Random Problems)](http://www.techiedelight.com/bit-hacks-part-6-random-problems/)
 
 ## Algorithms
 
@@ -174,9 +176,6 @@
 ## To Do
 
 - Bits Manipulation
-    - [ ] [Bit Hacks — Part 4 (Playing with letters of English alphabet)](http://www.techiedelight.com/bit-hacks-part-4-playing-letters-english-alphabet/)
-    - [ ] [Bit Hacks — Part 5 (Find absolute value of an integer without branching)](http://www.techiedelight.com/bit-hacks-part-5-find-absolute-value-integer-without-branching/)
-    - [ ] [Bit Hacks — Part 6 (Random Problems)](http://www.techiedelight.com/bit-hacks-part-6-random-problems/)
     - [ ] [Brian Kernighan’s Algorithm to count set bits in an integer](http://www.techiedelight.com/brian-kernighans-algorithm-count-set-bits-integer/)
     - [ ] [Compute parity of a number using lookup table](http://www.techiedelight.com/compute-parity-number-using-lookup-table/)
     - [ ] [Count set bits using lookup table](http://www.techiedelight.com/count-set-bits-using-lookup-table/)

src/binary/letters/UpperLowercaseSwapper.java

@@ -0,0 +1,43 @@
+package binary.letters;
+
+public class UpperLowercaseSwapper {
+    public static void main(String[] args) {
+        // to lowercase
+        for (char ch = 'A'; ch <= 'Z'; ch++) {
+            System.out.print((char) (ch | ' ')); // OR space
+        }
+        System.out.println();
+        // to uppercase
+        for (char ch = 'a'; ch <= 'z'; ch++) {
+            System.out.print((char) (ch & '_')); // AND underscore
+        }
+
+        /* Why does this work?
+        * Character	ASCII (Decimal)	ASCII (Binary)  Changes
+            'A'	    65	            01000001
+            'a'	    97	            01100001        'A' → 'a' adds 32 → sets bit 5 (counting from 0)
+            ' '	    32	            00100000        OR'ing with space sets bit 5, XOR'ing with space flips bit 5 so swaps the case
+            '_'	    95	            01011111        AND'ing with underscore clears bit 5
+        * */
+
+        System.out.println();
+        System.out.println();
+        // to invert
+        // lowercase uppercase
+        for (char ch = 'a'; ch <= 'z'; ch++) {
+            System.out.print((char) (ch ^ ' ')); // XOR space
+        }
+        System.out.println();
+        // same for uppercase to lowercase
+        for (char ch = 'A'; ch <= 'Z'; ch++) {
+            System.out.print((char) (ch ^ ' ')); // XOR space
+        }
+
+        System.out.println();
+        System.out.println();
+        // find letter's position in alphabet - AND 31
+        for (char ch = 'a'; ch <= 'z'; ch++) {
+            System.out.println(ch + " is in alphabet index " + (ch & 31)); // AND 31 (00011111)
+        }
+    }
+}