How to decrement a character value alphabetically in C++

Question

Is there a way to decrement a character value alphabetically in C++?

For example, changing a variable containing 'b' to the value 'a' or a variable containing 'd' to the value 'c' ?

I tried looking at character sequence but couldn't find anything useful.

Answer 1

Characters are essentially one byte integers (although the representation may vary between compilers). While there are many encodings which map integer values to characters, almost all of them map 'a' to 'z' characters in successive numerical order. So, if you wanted to change the string "aaab" to "aaaa" you could do something like the following:

char letters [4] = {'a','a','a','b'};
letters[3]--;

Answer 2

Alphabet characters are part of the ASCII character table. 65 is uppercase letter A, and 32 bits later, which is 97, is lowercase letter A. Letters B through Z and b through z are 66 through 90 and 98 through 122, respectively) The original computer programmers made it 32 bits apart in the ASCII chart rather than 26 (letters in the alphabet) because bit manipulation can be done to either easily change from lowercase to uppercase (and vice-versa), as well as ignoring the case (by ignoring the 32 bit - 0010 0000).

This way, for example, the 84th character on the ASCII chart, which represents the letter T, is represented with the bits 0101 0100. Lowercase t is 116 which is 0111 0100. When ignoring the case, the 1 in the 32 bit (6th position from the right) is ignored. You can see all the other bits are exactly the same for uppercase and lowercase. This makes it more convenient for everyone and more optimal for the computer.

To decrement just convert the character to its ASCII character value, decrement by 1, then take that integer and convert it back into ASCII value. Be careful when you have an 'A' though (or 'a'), as that's a special case.