A character ('char') variable can only contain one character:
char one_character = 'X';
An integer ('int') variable can contain up to two characters:
int two_characters = 'XY';
A long integer ('long') variable can contain up to four characters:
long four_characters = 'WXYZ';
A character array can contain a string of characters:
char string[] = "XYZABCDEFG";
(Note the use of double-quotes for a "string of characters" and the single quotes for 'character constants'. An additional character of value 0 is added to the string to mark the end.)
Any of them can be made constant by adding the 'const' keyword.