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

Last Updated : 18 Apr, 2024

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:

CPP

// 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;  }

Java

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));     } }

Python3

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))

JavaScript

// 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();

Output

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:

CPP

// 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;  }

Java

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));     } }

Python3

# 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))

JavaScript

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));

Output

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 .