Please enable JavaScript.

Coggle requires JavaScript to display documents.

Control Structures - Coggle Diagram

- - - - Two-way election
        
        if-then-else" statement
        
        Only one of the clauses is executed
        
        Under no circumstances both clauses are executed
        
        Nesting Selectors - Can be interpreted in two different ways depending on whether the else clause is matched with the first then clause or the second
        
        The statements could be single or compound
        
        In languages such as Ada, Java, Ruby, and C#, the control
        
        expression must be explicitly Boolean
      - N-way (multiple) selection
        
        "pascal case'', "Switch"
        
        A generalization of a selector.
        
        Allows selection of one of any number of statements or statement
        
        groups
        
        In C, C++, and Java switch expression must be of integer type
        
        Not encapsulated (selectable segments could be anywhere).
        
        Not encapsulated (selectable segments could be anywhere).
      - Single-way selection
        
        If statement
        
        Can select only a single statement; to select more, a goto must be used
    - - Continue
        
        Program control is passed from the continue statement to the end
        of the loop body
        
        A continue statement can only appear within the body of an
        iterative statement, such as do, for, or while
      - goto
        
        Performs a one-way transfer of control to another line of code.
        
        Improper usage may result in highly unreadable and difficult-to-maintain programs
        
        Labels
        
        A label is an explicit name or number (variable) assigned to a fixed position within the source code
        
        The label may be referenced by control flow statements appearing
        elsewhere in the source code
        
        In some new languages goto are completely eliminated.
        
        Some languages do not support goto statement (e.g., Java)
      - Break
        
        Let's end an iterative (do, for, or while) statement or a switch
        statement and exit from it at any point other than the logical end.
        
        In Java, the break statement has two forms: labeled and unlabeled
    - - Logically controlled loops
        
        Repetition control is based on a boolean expression
        
        Every counter controlled loop can be built with a logically controlled loop, but not the converse
      - Counter-controlled loops
        
        Has a variable: loop variable
        
        Some means of specifying the initial and terminal values of the loop variable, and the difference between sequential loop Variable values: Step size
        
        Pascal for statement
        
        Syntax: for var:= initial (to | downto) final do statement
        
        Loop var must be an ordinal type of usual scope
        
        After normal termination, loop var is undefined
        
        The loop var cannot be changed in the loop
        
        The loop parameters can be changed, but they are evaluated just once, so it does not affect loop control
        
        Ada for statement
        
        Syntax: for var in [reverse] discrete_range loop ........end loop;
        
        Type of the loop var is that of the discrete range; its scope is the loop body (it is implicitly declared)
        
        The loop var does not exist outside the loop.
        
        The loop var cannot be changed in the loop, but the discrete range can; it does not affect loop
        control
        
        The discrete range is evaluated just once
        
        FORTRAN 77 & 90 DO loop
        
        Loop variable can be an integer, real or double. Loop parameters can be expressions and can evaluated to negative values.
        
        Loop parameters are evaluated once at the beginning of the execution to generate an iteration count, after which loop parameters may be changed inside the loop
        
        Syntax is the same but semantics are different.
        
        C & C++ for statement
        
        Syntax: for( initialisation;pre_loop_expr ; post_loop_expr) statement;
        
        Multiple statements may be used in a single expression in a for loop, separated by comma.
        
        C’s for loop may contain both count and logical tests
        
        FORTRAN IV Do loop
        
        Loop parameters must be positive integers
        
        Loop variable is undefined upon existing loop, but is defined upon abnormal termination.
        
        Loop parameters cannot be changed inside the loop
        
        Syntax:
        DO label1 variable = initial, terminal, [stepsize]
      - Iteration based on data structures
        
        Rather than a counter or boolean expression controlling the iteration, a data structure is used to control the iteration . Number of iterations is controlled by the number of elements in the data structure.
      - Simple repetition
        
        Statement head specifies that the body is to be executed some
        fixed number of times.
      - User defined iteration control
        
        A more general databased iteration statement users a user-defined data structure and a user-defined function, called an iterator, to go through the structure’s elements
        
        Iterator -
        
        The iterator is called at the beginning of each iteration
        
        Each time it is called, the iterator returns an element from a particular data structure in some specific order
        
        Must be history sensitive
      - User located loop control mechanism
        
        When neither of the optional parts are defined, exit causes the termination of only the loop in which it appears
        
        Any loop can be labeled, and when a loop label is included in the exit, control is transferred to the statement immediately following the referenced loop.
        
        Several languages have loop statements that have no iteration control mechanism: they are infinite loops unless controlls are added by the programmer.