[Solved] can someone please elaborate the following code?

Question

The line:

ch[i] = (char)(ch[i] - 'a' + 'A');

Sets ch[i] to its associated uppercase due to a constant difference between an uppercase letter and its lowercase form.

For means of communication, the line can be re-written as:

ch[i] = (char)(ch[i] + ('A' - 'a'));

By adding this constant difference the line yields the lowercase letter’s uppercase character.

Accepted Answer

The line:

ch[i] = (char)(ch[i] - 'a' + 'A');

Sets ch[i] to its associated uppercase due to a constant difference between an uppercase letter and its lowercase form.

For means of communication, the line can be re-written as:

ch[i] = (char)(ch[i] + ('A' - 'a'));

By adding this constant difference the line yields the lowercase letter’s uppercase character.