This C program uses enumerated types to display days of week. The enumerated type is then declared as a different name using typedef keyword i.e. enum days to typedef enum days days.

The program has two functions, yesterday() and tomorrow() to calculate the previous and next days based on the current day. These functions handle the circular nature of the days to ensure that correct results is displayed. An array of constant strings, thedays, stores the names of the days of the week.

The function prints for each day of the week, today, yesterday, and tomorrow, both as a string and as a number.

The output of the above program is: