Lower case to upper case – An interesting fact

Difficulty Level : Easy
Last Updated : 12 Jun, 2021

Problem: Given a string containing only lowercase letters, generate a string with the same letters, but in uppercase.

Input : GeeksForGeeks
Output : GEEKSFORGEEKS

The first method that comes to our mind is

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C++

// C++ program to convert a string to uppercase
#include <iostream>
using namespace std;
 
// Converts a string to uppercase
string to_upper(string &in)
{
    for (int i = 0; i < in.length(); i++)
          if ('a' <= in[i] <= 'z')
              in[i] = in[i] - 'a' + 'A';
    return in;
}
 
// Driver code
int main()
{
   string str = "geeksforgeeks";
   cout << to_upper(str);
   return 0;
}

Java

// Java program to convert a string to uppercase
 
class GFG
{
 
    // Converts a string to uppercase
    static String to_upper(char[] in)
    {
        for (int i = 0; i < in.length; i++)
        {
            if ('a' <= in[i] & in[i] <= 'z')
            {
                in[i] = (char) (in[i] - 'a' + 'A');
            }
        }
        return String.valueOf(in);
    }
 
    // Driver code
    public static void main(String[] args)
    {
        String str = "geeksforgeeks";
        System.out.println(to_upper(str.toCharArray()));
    }
}
 
// This code is contributed by PrinciRaj1992

Python3

# Python3 program to convert a string to uppercase
 
# Converts a string to uppercase
def to_upper(string):
    for i in range(len(string)):
        if ('a' <= string[i] <= 'z'):
            string = (string[0:i] + chr(ord(string[i]) -
                                        ord('a') + ord('A')) +
                                        string[i + 1:])
    return string;
 
# Driver code
if __name__ == '__main__':
    str = "geeksforgeeks";
    print(to_upper(str));
 
# This code is contributed by Rajput-Ji

C#

// C# program to convert a string to uppercase
using System;
 
class GFG
{
    // Converts a string to uppercase
    static String to_upper(char []In)
    {
        for (int i = 0; i < In.Length; i++)
        {
            if ('a' <= In[i] & In[i] <= 'z')
            {
                In[i] = (char) (In[i] - 'a' + 'A');
            }
        }
        return String.Join("", In);
    }
 
    // Driver code
    public static void Main()
    {
        String str = "geeksforgeeks";
        Console.WriteLine(to_upper(str.ToCharArray()));
    }
}
 
// This code is contributed by 29AjayKumar

Javascript

<script>
      // JavaScript program to convert a string to uppercase
      // Converts a string to uppercase
      function to_upper(input)
      {
        var result = new Array(input.length);
        for (var i = 0; i < input.length; i++)
          if ("a".charCodeAt(0) <= input[i].charCodeAt(0) <= "z".charCodeAt(0))
            result[i] = String.fromCharCode(
              input[i].charCodeAt(0) - "a".charCodeAt(0) + "A".charCodeAt(0)
          );
 
        return result.join("").toString();
      }
 
      // Driver code
      var str = "geeksforgeeks";
      document.write(to_upper(str));
       
      // This code is contributed by rdtank.
    </script>

Output :

GEEKSFORGEEKS

A more interesting solution, on the other hand, would be:

C++

// C++ program to convert a string to uppercase
#include <iostream>
using namespace std;
 
// Converts a string to uppercase
string to_upper(string &in)
{
    for (int i = 0; i < in.length(); i++)
          if ('a' <= in[i] <= 'z')
              in[i] &= ~(1 << 5);
    return in;
}
 
// Driver code
int main()
{
   string str = "geeksforgeeks";
   cout << to_upper(str);
   return 0;
}

Java

// Java program to convert a string to uppercase
class GFG
{
 
// Converts a string to uppercase
static String to_upper(char[] in)
{
    for (int i = 0; i < in.length; i++)
        if ('a' <= in[i] && in[i] <= 'z')
            in[i] &= ~(1 << 5);
    return String.valueOf(in);
}
 
// Driver code
public static void main(String[] args)
{
    String str = "geeksforgeeks";
    System.out.println(to_upper(str.toCharArray()));
}
}
 
// This code is contributed by Rajput-Ji

Python3

# Python3 program to convert
# a string to uppercase
 
# Converts a string to uppercase
def to_upper(s):
    for i in range(len(s)):
        if ('a' <= s[i] <= 'z'):
            s = s[0:i] + chr(ord(s[i]) & \
                            (~(1 << 5))) + s[i + 1:];
    return s;
 
# Driver code
if __name__ == '__main__':
    string = "geeksforgeeks";
    print(to_upper(string));
 
# This code is contributed by PrinciRaj1992

C#

// C# program to convert a string to uppercase
using System;
 
class GFG
{
 
// Converts a string to uppercase
static String to_upper(char[] str)
{
    for (int i = 0; i < str.Length; i++)
        if ('a' <= str[i] && str[i] <= 'z')
            str[i] = (char)((int)str[i]&(~(1 << 5)));
    return String.Join("", str);
}
 
// Driver code
public static void Main(String[] args)
{
    String str = "geeksforgeeks";
    Console.WriteLine(to_upper(str.ToCharArray()));
}
}
 
// This code is contributed by PrinciRaj1992

Javascript

<script>
 
// Javascript program to convert
// a string to uppercase
 
// Converts a string to uppercase
function to_upper(In)
{
    let n = In.length;
    for(let i = 0; i < In.length; i++)
        if ('a' <= In[i] && In[i] <= 'z')
            In[i] = String.fromCharCode(
                In[i].charCodeAt(0) & (~(1 << 5)));
                 
    return (In).join("");
}
 
// Driver code
let str = "geeksforgeeks";
 
document.write(to_upper(str.split("")));
 
// This code is contributed by rag2127
 
</script>

Output :

GEEKSFORGEEKS

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. The only difference is the sixth bit, setted only for lowercase letters. What that elegant function does is unset the bit of index 5 of in[i], consequently, making that character lowercase.

Disadvantages: That strategy works only for alphabetical characters. If the input contains numbers or punctuations, we’ll have to use the naive way.

Example: Character ‘A’ is integer 65 = (0100 0001)2, while character ‘a’ is integer = 97 = (0110 0001)₂. (Note that 97 – 65 = 32. Can you guess why?)

Exercises:

Write a function to make all letters of a string lowercase. Example: GeeksForGeeks turns geeksforgeeks.
Write a function that change the case of a string. Example: GeeksForGeeks turns gEEKSfORgEEKS.

This article is contributed by Igor Carpanese. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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