Case conversion (Lower to Upper and Vice Versa) of a string using BitWise operators in C/C++

Given a string, write a function that converts it either from lower to upper case or from upper to lower case using the bitwise operators &(AND), |(OR), ~(NOT) in place and returns the string. Many of us know that Bitwise manipulations are faster than performing arithmetic operations for a compiler as the data is stored in binary form 0's and 1's. Examples:

Input : "LowerToUpPer"
Output : "LOWERTOUPPER"
 Letters already in the uppercase remains the same. 
 while rest get converted to uppercase.

Input : "UPPerTOloweR"
Output : "uppertolower"
 Letters already in the lowercase remains the same.
 while rest get converted to lowercase.

1.Lower to Upper Case This method simply subtracts a value of 32 from the ASCII value of lowercase letter by Bitwise ANDing (&) with negation (~) of 32 converting the letter to uppercase. 

Implementation:

// C++ program to convert a string from  // lower to upper case.  #include<stdio.h>  const int x = 32;  // Converts a string to uppercase  char *toUpperCase(char *a)  {   for (int i=0; a[i]!='\0'; i++)   a[i] = a[i] & ~x;   return a;  }  // Driver Code  int main()  {   char str[] = "SanjaYKannA";   //Here it's recommended to use character array   //as it's stored in read-write area.   //If a pointer is used it's stored   //in read-only memory as a string literal.   printf("%s", toUpperCase(str));   return 0;  }  

public class Main {  static final int x = 32;  // Converts a string to uppercase  static String toUpperCase(String a) {  char[] chars = a.toCharArray();  for (int i = 0; i < chars.length; i++) {  chars[i] = (char) (chars[i] & ~x);  }  return new String(chars);  }  // Driver Code  public static void main(String[] args) {  String str = "SanjaYKannA";  // Here it's recommended to use a String  // as it's stored in the heap area.  // If a char array is used, it's stored  // in the stack as a string literal.  System.out.print(toUpperCase(str));  } } 

def to_upper_case(s): result = "" for char in s: if 'a' <= char <= 'z': result += chr(ord(char) & ~32) else: result += char return result # Driver code str = "SanjaYKannA" print(to_upper_case(str)) 

// Converts a string to uppercase function toUpperCase(str) {  let result = '';  const x = 32; // ASCII difference between uppercase and lowercase letters  for (let i = 0; i < str.length; i++) {  const charCode = str.charCodeAt(i);  // Convert lowercase letters to uppercase by adding the ASCII difference  // Note: this assumes the input string only contains lowercase letters  result += String.fromCharCode(charCode & ~x);  }  return result; } // Driver Code function main() {  const str = "SanjaYKannA";  console.log(toUpperCase(str)); } main(); 

SANJAYKANNA

Time complexity : O(n) 
Auxiliary Space : O(1) 

2.Upper to Lower Case Similarly, it adds a value of 32 to the ASCII value of uppercase letter by Bitwise ORing (|) with 32 converting the letter to lowercase. 

Implementation:

// C++ program to convert a string from  // upper to lower case.  #include<stdio.h>  const int x = 32;  // Converts a string to lowercase  char * toLowerCase(char *a)  {   for (int i=0; a[i]!='\0'; i++)   a[i] = a[i] | x;   return a;  }  // Driver Code  int main()  {   char str[] = "SanjaYKannA";   printf("%s", toLowerCase(str));   return 0;  }  

public class Main {  // Constant value for converting uppercase to lowercase  static final int x = 32;  // Converts a string to lowercase  static String toLowerCase(String str) {  char[] chars = str.toCharArray();  // Iterate through each character in the string  for (int i = 0; i < chars.length; i++) {  // Check if the character is an uppercase letter  if (Character.isUpperCase(chars[i])) {  // Convert the uppercase letter to lowercase using ASCII manipulation  chars[i] = (char) (chars[i] | x);  }  }  // Convert the character array back to a string and return  return new String(chars);  }  // Main method  public static void main(String[] args) {  // Input string  String str = "SanjaYKannA";  // Convert the string to lowercase and print  System.out.println(toLowerCase(str));  } } 

# code def gfg(string): # Initialize an empty string to store the lowercase result result = '' # Loop through each character in the input string for char in string: # Check if the character is uppercase if 'A' <= char <= 'Z': result += chr(ord(char) + 32) else: # If the character is not uppercase, add it to the result as it is result += char # Return the resulting lowercase string return result # Test the function string = "SanjaYKannA" print(gfg(string)) 

function GFG(str) {  // Initialize an empty string to the store the lowercase result  let result = '';  // Loop through each character in input string  for (let i = 0; i < str.length; i++) {  // Check if the character is uppercase  if (str[i] >= 'A' && str[i] <= 'Z') {  result += String.fromCharCode(str.charCodeAt(i) + 32);  } else {  // If the character is not uppercase, add it to result as it is  result += str[i];  }  }  // Return the resulting lowercase string  return result; } // Test the function let str = "SanjaYKannA"; console.log(GFG(str)); 

sanjaykanna

Time complexity : O(n) 
Auxiliary Space : O(1) 

Explanation: The ASCII table is constructed in such way that the binary representation of lowercase letters is almost identical of binary representation of uppercase letters. Character ‘A’ is integer 65 = (0100 0001)2, while character ‘a’ is integer 97 = (0110 0001)2. The difference between the ASCII values of 'a' and 'A' is 32. So we can easily change the case of the letters either from Upper to lower or lower to upper by adding or subtracting the difference from the letters using bitwise operators as shown above. 

Exercise: Implement a function that change the case of a string such that GeeksFoRgeekS turns gEEKSfOrGEEKs .