To specify a single character, use either char or unsigned char. C was developed in the time before Unicode. The character set they decided upon using was ASCII (short for American Standard Code for Information Interchange). All the necessary characters for printing control, device control, and printable characters and punctuation could be represented in 7 bits.
One reason ASCII was chosen was because of its somewhat logical ordering of uppercase and lowercase letters. An uppercase A and lowercase a are different by only 1 bit. This makes it relatively easy to convert from uppercase to lowercase and vice versa. There is an ASCII table provided for your reference in the Appendix; we also develop a program to print a complete ASCII table in Chapter 15, Working with Strings.
To summarize ASCII's organization, refer to the following table:
Range | ...