# 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 : techcodebit
Output : TECHCODEBIT```

The first method that comes to our mind is

`// 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 = ``"<a href="``#``">techcodebit</a>"``;`
`   ``cout << to_upper(str);`
`   ``return` `0;`
`}`

Output :

`TECHCODEBIT`

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

`// 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 = ``"<a href="``#``">techcodebit</a>"``;`
`   ``cout << to_upper(str);`
`   ``return` `0;`
`}`

Output :

`TECHCODEBIT`

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.

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?)

Disclaimer: This does not belong to TechCodeBit, its an article taken from the below
source and credits.
source and credits:http://www.geeksforgeeks.org/lower-case-upper-case-interesting-fact/
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