C Language Q & A #11 (cont.)

A char variable can hold a single byte (eight bits) of information, so an assignment of ch = ASCII_X; would be converted to ch = ‘X’; by the preprocessor. ‘X’ is a character constant, and you can assign it’s value to a character variable.
If you change the definition to #define ASCII_X ‘SX’, the assignment would look like ch = ‘SX’; Since a char variable can only hold one byte of data, it takes the ‘S’, and ignores the ‘X’.