The importance of c enumeration (typedef enum) [duplicate]

Question

I recently saw this in an answer that was posted for me:

typedef enum {     NO_OP,     ADDITION, } operator_t;  int main() {     operator_t operator = NO_OP; } 

What is typedef enum and why should we use it? I googled and found the following: http://www.programiz.com/c-programming/c-enumeration

Right now it sounds slightly too technical for me so I don't think I understand what is going on or why anyone would use that.

Bonus (optional): What type of variable is the operator_t?

Answer 1

1. It's definitely not "too technical".

2. "typedef" and "enum" are two completely different things.

3. The basic reason to have "enums" is to avoid "magic numbers":

   Let's say you have three "states": STOP, CAUTION and GO. How do you represent them in your program?

   One way is to use the string literals "STOP", "CAUTION" and "GO". But that has a lot of problems - including the fact that you can't use them in a C "switch/case" block.

   Another way is to Map" them to the integer values "0", "1" and "2". This has a lot of benefits. But seeing "STOP" in your code is a lot more meaningful than seeing a "0". Using "0" in your code like that is an example of a "magic number". Magic numbers are Bad: you want to use a "meaningful name" instead.

Before enums were introduced in the language, C programmers used macros:

   #define STOP 0    #define CAUTION 1    #define GO 2 

A better, cleaner approach in modern C/C++ is to use an enum instead:

enum traffic_light_states {   STOP,   CAUTION,   GO };  

Using a "typedef" just simplifies declaring a variable of this type:

typedef enum {   STOP,   CAUTION,   GO } traffic_light_states_t ;  

Answer 2

typedef is used to define an alternative name for an existing type. The enum could have declared like this:

enum operator_t {     NO_OP,     ADDITION, }; 

and then you could declare a variable of this type like so:

enum operator_t x = NO_OP; 

This is kind of verbose so you would use typedef to define a shorter alias for this type:

typedef enum operator_t operator_t; 

This defines operator_t to mean the type enum operator_t allowing you to initialize a variable like so:

operator_t x = NO_OP; 

This syntax:

typedef enum {     NO_OP,     ADDITION, }   operator_t; 

does the whole process in one step, so it defines an (untagged or tagless) enum type and gives it the alias operator_t.

Bonus: operator_t is an enum data type; read more about it here: https://en.wikipedia.org/wiki/Enumerated_type