Chapter 11.11, Problem 11.20CP

Program Plan Intro

Union:

In C++, the union is a user-define data type, which contains different type of elements with different lengths.

• It uses single memory location to hold more than one variable. It takes the memory of the largest data type.
• It conserves memory as it stores all the members in the same memory location.
• Union variable can initialize in main function within the program. Then initialize the union members using the union variable.
• Union variable can be declared in the type of array and the entire array elements can be accessed through a loop.

 Declaration of union:

The declaration of union is the same as a structure with the only difference that, instead of using a keyword “struct”, the keyword “union” should be used.

Example:

union Score

{

int rollNo;

float marks;

};

The “Score” is the union variable which is defined with the two members:  “rollNo( a int)” and “marks (a float)”. The union variable will take up as much memory as the largest member.

Declaration of union for the given members:

Declaration of union for the “letter”, “whole”, “real” members are given as follows:

union ThreeTypes

{

char letter;

int whole;

double real

};

The “ThreeTypes” is the union variable which is defined with three members: “letter” as “char”, “whole” as “int” and “real” as “double”.

• The union variable “ThreeTypes” will only take up the memory of “double” as it holds the largest size when compared to the “int” and “char” data types.
• The size of the “double” is 4 bytes and the size of the “int” is 2 bytes and that of “char” is 1 byte.

Defining an array for union:

An array of union can be defined in the form of an array which is used to implement multiple values in a union. It can be accessed through its index value.

Definition of an array of union for the above “ThreeTypes”:

ThreeTypes values [50];

The “values” is a variable in the type of union “ThreeTypes”. The size of the “values” is “50”.

 “for” loop:

In some cases it is necessary to track number of times the loop gets executed. So C++ provides such type of control loop is known as “for” loop.

• “for” loop is also referred as count-controlled loop; it contains three process as follows:
  • Initialization
  • Compare and
  • Update
• It is possible to initialize more than one variable in loop expression.

Syntax:

The syntax for the “for” loop is as follows:

//for loop condition

for (initialization; Compare; Update)

{

//statement

}