The union is a construct that allows memory to be shared by different types of data. This redefinition can be as simple as redeclaring an integer as four characters or as complex as redeclaring an entire structure.
Topics discussed in this section:
Referencing Unions
Initializers
Unions and Structures
Internet Addresses
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FIGURE 12-20 Unions
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PROGRAM 12-7 Demonstrate Effect of Union
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PROGRAM 12-7 Demonstrate Effect of Union
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FIGURE 12-21 A Name Union
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PROGRAM 12-8 Demonstrate Unions in Structures
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PROGRAM 12-8 Demonstrate Unions in Structures
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PROGRAM 12-8 Demonstrate Unions in Structures
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PROGRAM 12-9 Convert IP Address to long
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PROGRAM 12-9 Convert IP Address to long
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PROGRAM 12-9 Convert IP Address to long
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In this section, we develop a program that simulates the operation of an elevator. The elevator serves floors from zero (the basement) to the top floor. The elevator is very old and is not fully automatic. When people enter the elevator, they enter their desired floor number.
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FIGURE 12-22 Elevator Structure
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FIGURE 12-23 Elevator Structure Chart
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FIGURE 12-24 Elevator State Diagram
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PROGRAM 12-10 Elevator: main
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PROGRAM 12-10 Elevator: main
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PROGRAM 12-11 Elevator: Initialize
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PROGRAM 12-12 Elevator: Run Elevator
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PROGRAM 12-12 Elevator: Run Elevator
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PROGRAM 12-12 Elevator: Run Elevator
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PROGRAM 12-13 Elevator: Move
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PROGRAM 12-13 Elevator: Move
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PROGRAM 12-13 Elevator: Move
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PROGRAM 12-14 Elevator: Move Up and Move Down
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PROGRAM 12-14 Elevator: Move Up and Move Down
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PROGRAM 12-14 Elevator: Move Up and Move Down
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PROGRAM 12-14 Elevator: Move Up and Move Down
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PROGRAM 12-15 Elevator: Any Up and Any Down Request
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PROGRAM 12-15 Elevator: Any Up and Any Down Request
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PROGRAM 12-16 Elevator: Time Pass
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PROGRAM 12-17 Elevator: Terminate
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In this section we discuss two important aspects of program design: function coupling and data hiding.
Topics discussed in this section:
Coupling
Data Hiding
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Note
Well-structured functions are highly cohesive and loosely coupled.
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Note
Stamp coupling should pass only the data needed.
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Note
Don’t bundle unrelated data to reduce the number of parameters.
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Note
Control coupling should be used only to pass status.
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Note
Avoid global coupling within a program.
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Note
Never use content coupling.
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Note
Programming Standard:
Do not place any variables in the global area of a program.
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