Properties of Variables

Question 1

What are the properties of storage duration

Answer 1

• Automatic - variable is allocated when the surrounding block is executed and deallocated when the block terminates
• Static - variable stays at the same storage location as long as the program is running

Question 2

What are the properties(options) of scope

Answer 2

• Block scope - variable is visibile from its point of declaration until the end of the block
• File scope - variable is visible frmo its point of delcaration until the end of the enclosing file

Question 3

What aer the properties of linkage?

Answer 3

• External linkage - variable may be shared with serveral or all files in a program
• Internal linkage - restricted to a single file and may not be shared
• No linkage - varialbe belongs to a single function and cannot be shared

Question 4

What is the default storage duration, scope and linkage of a variable?

Answer 4

Question 5

What are the properties of the auto storage class?

Answer 5

auto is legal only for variables that belong to a block

has automatic storage duration, block scope and no linkage

Question 6

What are the properties of the static storage class:

When used outside of a block?

When used inside of a block?

Answer 6

• When used outside a block, static has internal linkage
• when used inside a block, static changes the storage duration from automatic to static
  
  • stays within the same storage location throughout program execution
  • shared for all calls of the function
• Is initialized once prior to program execution

Question 7

What are the benefits of the extern storage class?

Answer 7

• Allows several source files to share the same variable
• doesn’t cause memory to be allocated for a variable
• It tells the compiler that it is defined elsewhere

Question 8

What are the properties of register storage class?

Answer 8

• Asks compiler to store the variable in the CPU register (high-speed storage area in CPU_
• Compiler is free to store a register variable in memory if it chooses
• Must be declared in a block
• same storage duration, scope and linkage as auto
• cannot use the & operator because it does not have a memory address
• best used for varialbes that are accessed or updated frequently
  
  • int i in a for loop is a good candidate

Question 9

What storage classes can functions have?

Answer 9

• extern - allows it to be called from other files (default)
• static - limits use of function to the file
  
  • future modifications won’t affect other files
  • names don’t conflict with other names in other files

static intg(int i);

Question 10

What are modules made up of?

Answer 10

• collection of services(functions), some of which are made available to other parts of the program(the clients)
• each module has an interface(a header file containing prototypes for the functions) that describes the available services
• The details of the module - including the source code for the services themselves - are stored in the modules implementation(contains definitions of the module’s functions)

Question 11

Using linked lists as an example, how do the modules work?

Answer 11

• teamLists.c - main (client of list module)
• lists.h and lists.c - list module
  
  • .h is interface of the list module
  • .c is the implementation of the module
• nodes.h and nodes.c - node module

Question 12

What are the advantages of dividing a program into modules?

Answer 12

• Abstraction
• Reusability
• Maintainability