Lecture 14: Subrograms and Parameter Passing

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what is a subprogram
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A subprogram is a piece code that is identified by a name, is given a local reference environment of its own and is able to exchange information with the rest of the code using parameters.

what two fundamental abstraction facilities do Subprograms/Functions provide
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Process/control abstraction, Data abstraction

explain Process/control abstraction:
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[1] Provides programmers with the ability to hide procedural details[2] Process abstraction allows us to be concerned only with a procedure’s interface[3]E. g given a procedure sort we don’t need to know the body of sort in order to use it.

explain Data abstraction
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Data abstraction: allows the use of sophisticated data types without knowing how such types are implemented. Again, the aims are to separate concerns and to promote reusability and maintainability of programs.

what is a formal parameter
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A formal parameter is a dummy variable listed in the function header and used in the function body.

what is an actual parameter
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An actual parameter represents a value or address used in the function call statement.

what is a return value
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Functions may exchange info with the rest of the program by a return value or through the use of parameters. s. n value

what are the 2 ways to bind parameters
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: by position or by keyword.

explain parameter binding by position
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By position: The binding of actual parameters to formal parameters is by their order of appearance: the first actual parameter is bound to the first formal parameter and so forth. x=foo(3, 0); Safe and effective.

eexplain parameter binding by keyword
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Keyword: The names of the formal and actual parameters are used Advantage: Parameters can appear in any order, thereby avoiding parameter correspondence errors. Disadvantage: User must know the formal parameters’ names.

what is in(put) mode in referance to Parameter Passing Methods
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Formal parameters receive data from the corresponding actual parameters.

what is out(put) mode in referance to Parameter Passing Methods
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Formal parameters transmit data to the actual parameters; or

what is inout) mode in referance to Parameter Passing Methods
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Formal parameters receive data from the corresponding actual parameters and Formal parameters transmit data to the actual parameters


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