Structs are a a type from C that C++ used as a template for classes. We will briefly look at structs since they define data (i.e., data members) the same way as classes do. However, classes also permit us to define methods (i.e, functions).

1. Single Records
   • Keyword struct used to define structure types; no space allocated for the type

     struct EMPLOYEE {
       int emp_no;
       char name[20];
       char address[40];
     };
     

   • To declare a variable and allocate space:

        struct EMPLOYEE  engineer;
     

   • The "struct" in the declaration is optional

        EMPLOYEE  engineer;
     

   • To initialize

        = {143, "George", "123 Main St."};
     

   • Or, declare a variable by placing it after the end "}" in the struct definition.
   • To access and element of a structure, use the dot notation: Engineer.emp_no = 9999;
2. Arrays of Records
   • An array of structures is declared as

       rec array[30];
       array[5].i = 8;
     

   • Or a 2-dimensional array

       struct rec array[3][4][2];
       array[2][3][1].i = 9;   /*The last element of the array */
     

3. Record Structures as Function Arguments
   • Call function with structure elements

       fn1(engineer.emp_no);  // call
       fn1 (int emp_no)	//header
     

   • Call function with entire structure

       fn2 (engineer);	//call
       fn2 (struct employee E) //header
     

   • Default pass by value, use & for pass by reference
   • Return a struct from a function

       Emp = fn3( );		// call
       struct employee fn3 ( )	//header
       	struct employee var;	// decl
       	return (var)		//return
     

4. Pointers to structures can also be used, and space must be allocated using new

     struct rec {
       int i;
       float f;
       char c;
      };
     rec *rec_ptr;
     rec_ptr = new struct rec;
   
     (*rec_ptr).i = 30;	/* or rec_ptr->i = 30  */
     rec_ptr->f = 1.234;
     rec_ptr->c = 'X';
     delete(rec_ptr);
   

5. Unions
   • When all elements of a structure are not needed, use a union

        union Number {
        	int i;
        	float f;
        };
     

   • A variable of type union can only be initialized with the first type

        union Number value = { 8};    /* 3.4 would be invalid */
     

   • A variable of type union Number can use only one of the components at a time.

        value.i = 100;
        cout <<  value.i;
        value.f = 123.45;
        cout <<  value.f;
     

6. Enumerated Types
   • Enumerated types can be declared:

        enum colors = { red, blue, green };
     

   • The enumerated values red == 0, blue ==1, and green == 2
   • Variables can be declared as:

        enum colors rainbow;		OR		COLORS rainbow;