Flashcards
Computing Unit 2 Chapter 2
Flashcards do conjunto (12)
- 1Statement• a single instruction (usually a single line of code) which can be executed.
• Some statements can contain others (eg IF, WHILE). - 2Subroutine• in the context of A-level computing, a generic term meaning either procedure or function.
• a separate sub-program that can be “called” from anywhere else in the code.
• execution jumps to the start of the subroutine then, when the subroutine finishes, execution returns to the point from which it was called.
• parameters may be passed to a subroutine, and these then act as variables within it. - 3Procedure• A subroutine which is given an identifier and can be called from the main program or from another subroutine.
• When called the code in the procedure is executed.
• Control is then passed back to where the procedure was called.
• Unlike a function, it does not return a value. - 4Function• is a subroutine that returns a single value.
• can be called using its identifier, which can then be used in expressions like a variable, with the value returned replacing the function call. - 5Parameter• a variable which holds an item of data which is passed to a subroutine, procedure or function.
• given an identifier when the subroutine is defined and substituted by an actual value when the subroutine is called. - 6SequenceA construct in which…
• all instructions are executed exactly once.
• instructions are executed in the order in which they appear. - 7SelectionA construct in which…
• a condition is used to determine which of the statements (if any) will be executed.
• As a result some instructions may not be executed. - 8Iteration / LoopA construct in which…
• A group of statements is executed repeatedly for a set number of times or until a condition is met. - 9Nesting• When a selection/iteration statement is enclosed within another selection/iteration statement.
• The nested statement must be ended before the end of the enclosing statement or a syntax error will be generated. - 10Recursion• This is when a function/procedure/subroutine calls itself.
• The original call is halted until subsequent calls return.
• Eventually a stopping condition must be reached. - 11When tracing programs…• refer to each line of code by number in the order in which it is executed.
• when expressions are evaluated, state the resulting value.
• record changes in the values of variables.
• in IF statements and WHILE loops, etc., state whether the expression evaluates to TRUE or FALSE and where execution will jump to as a result.
• in calls to subroutines, functions and procedures, state the value(s) (if any) that are passed.
• when a function ends, state the value that is returned. - 12Iteration vs RecursionAdvantages of iteration:
• Iteration uses only one set of variables (which are updated on each loop), whereas recursion creates new variables for each call.
• Iteration makes more efficient use of memory.
• Iteration can be faster.
• Iteration is less likely to run out of stack space than recursion.
Disadvantages of iteration:
• The algorithm may be more difficult to follow/trace because variables are being reused.
• You need to be careful to get the conditions of loops correct (given current state of variables).
• Humans often express the problem in a recursive way.
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- FlashCards sobre Computing Unit 2 Chapter 2, criado por jacksinoxu em 23-03-2015.
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