Lower case to upper case – An interesting fact

16 Jun, 2022
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  
C++
Java
Python3
C#
Javascript
// C++ program to convert a string to uppercase#include <iostream>using namespace std; // Converts a string to uppercasestring 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 codeint main(){   string str = "geeksforgeeks";   cout << to_upper(str);   return 0;}
// 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 program to convert a string to uppercase # Converts a string to uppercasedef 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 codeif __name__ == '__main__':    str = "geeksforgeeks";    print(to_upper(str)); # This code is contributed by Rajput-Ji
// C# program to convert a string to uppercaseusing 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
<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>
GEEKSFORGEEKS
Time Complexity: O(n),where n is length of string.
Auxiliary Space: O(1)
A more interesting solution, on the other hand, would be: 
C++
Java
Python3
C#
Javascript
// C++ program to convert a string to uppercase#include <iostream>using namespace std; // Converts a string to uppercasestring to_upper(string &in){    for (int i = 0; i < in.length(); i++)          if ('a' <= in[i] <= 'z')              in[i] &= ~(1 << 5);    return in;} // Driver codeint main(){   string str = "geeksforgeeks";   cout << to_upper(str);   return 0;}
// Java program to convert a string to uppercaseclass GFG{ // Converts a string to uppercasestatic 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 codepublic static void main(String[] args){    String str = "geeksforgeeks";    System.out.println(to_upper(str.toCharArray()));}} // This code is contributed by Rajput-Ji
# Python3 program to convert# a string to uppercase # Converts a string to uppercasedef 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 codeif __name__ == '__main__':    string = "geeksforgeeks";    print(to_upper(string)); # This code is contributed by PrinciRaj1992
// C# program to convert a string to uppercaseusing System; class GFG{ // Converts a string to uppercasestatic 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 codepublic static void Main(String[] args){    String str = "geeksforgeeks";    Console.WriteLine(to_upper(str.ToCharArray()));}} // This code is contributed by PrinciRaj1992
<script> // Javascript program to convert// a string to uppercase // Converts a string to uppercasefunction 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 codelet str = "geeksforgeeks"; document.write(to_upper(str.split(""))); // This code is contributed by rag2127 </script>
GEEKSFORGEEKS
Time Complexity: O(n),where n is length of string.
Auxiliary Space: O(1)
Method 3(using C++ STL)
In C++ STL there is a function called “transform” which converts the case of all latter of a string.
Below is an implementation of that function:
C++
//C++ code to transform the string's//latter to uppercase english alphabet.#include<bits/stdc++.h>using namespace std;void transform_to_upper(string &s){    //in-built C++ STL function    //which transform the string    //to uppercase    transform(s.begin(),s.end(),s.begin(),::toupper);    cout<<"string with uppercase latter is: "<<endl;    cout<<s;} //driver codeint main() {string s="GeeksForGeeks";//function calltransform_to_upper(s);return 0;} //this code is contributed by Machhaliya Muhammad
string with uppercase latter is: 
GEEKSFORGEEKS
Time Complexity: O(n),where n is length of string.
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. 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.
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.
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