Characters consists of any keyboard symbol, and several other symbols.
When presented as a constant in a program, the character is surrounded by single quotes to distinguish the symbol from a variable or number. Traditionally, a char is recorded in one byte. So there are 255 different character codes , though not each of these codes is actually associated with a keyboard character. There are some nice features of those code you can use in your programming. The lower case letters are also consecutive, as are the upper case.