UNION

1. C Unions are essentially the same as C Structures
2. except that instead of containing multiple variables each with their own memory a Union allows for multiple names to the same variable
3. that means it allocatees the memory equal to the size of the variable of the maximum size.
4. These names can treat the memory as different types.

Combining this with a structure allows you to create a “tagged” union which can be used to store multiple different types, one at a time.

For example, you might have a “number” struct, but you don’t want to use something like this:

struct operator {
    int intNum;
    float floatNum;
    int type;
    double doubleNum;
};

Because your program has a lot of them and it takes a bit too much memory for all of the variables

struct operator {
    int type;
    union {
      int intNum;
      float floatNum;
      double doubleNum;
    } types;
};