# Lower case to upper case – An interesting fact

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

```Input : GeeksForGeeks
Output : GEEKSFORGEEKS ```
Recommended Practice

The first method that comes to our mind is

## C++

 `// C++ program to convert a string to uppercase` `#include ` `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

 ``

Output

`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++

 `// C++ program to convert a string to uppercase` `#include ` `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

 ``

Output

`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` `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: "``<

## Java

 `import` `java.util.*;`   `public` `class` `Main {` `  ``public` `static` `void` `transformToUpper(StringBuilder s) ` `  ``{`   `    ``// In-built Java function that transforms the string to uppercase` `    ``s = ``new` `StringBuilder(s.toString().toUpperCase());` `    ``System.out.println(``"String with uppercase letters is:"``);` `    ``System.out.println(s);` `  ``}`   `  ``// driver code` `  ``public` `static` `void` `main(String[] args) {` `    ``StringBuilder s = ``new` `StringBuilder(``"GeeksForGeeks"``);`   `    ``// function call` `    ``transformToUpper(s);` `  ``}` `}`

## Python3

 `# Python implementation of above approach`   `# Python code to transform the string's` `# letters to uppercase English alphabet.`   `def` `transform_to_upper(s):` `    ``# In-built Python function` `    ``# which transforms the string` `    ``# to uppercase` `    ``s ``=` `s.upper()` `    ``print``(``"String with uppercase letters is: "``)` `    ``print``(s)`   `# Driver code` `if` `__name__ ``=``=` `'__main__'``:` `    ``s ``=` `"GeeksForGeeks"` `    ``# Function call` `    ``transform_to_upper(s)`     `# This code is contributed by codebraxnzt`

## C#

 `using` `System;` `using` `System.Text;`   `public` `class` `MainClass {` `  ``public` `static` `void` `TransformToUpper(StringBuilder s) ` `  ``{` `    ``// In-built C# function that transforms the string to uppercase` `    ``s = ``new` `StringBuilder(s.ToString().ToUpper());` `    ``Console.WriteLine(``"String with uppercase letters is:"``);` `    ``Console.WriteLine(s);` `  ``}`   `  ``// driver code` `  ``public` `static` `void` `Main(``string``[] args) {` `    ``StringBuilder s = ``new` `StringBuilder(``"GeeksForGeeks"``);`   `    ``// function call` `    ``TransformToUpper(s);` `  ``}` `}`

## Javascript

 `// JavaScript implementation of above approach`   `// JavaScript function to transform the string's` `// letters to uppercase English alphabet.`   `function` `transformToUpperCase(s) {` `  ``// In-built JavaScript function` `  ``// which transforms the string` `  ``// to uppercase` `  ``s = s.toUpperCase();` `  ``console.log(``"String with uppercase letters is: "``);` `  ``console.log(s);` `}`   `// Driver code` `const s = ``"GeeksForGeeks"``;` `// Function call` `transformToUpperCase(s);`

Output

```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:

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

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