Program Constructs: Iteration & Recursion

Nesting

When a construct is written completely contained within another. They are not allowed to overlap.

Recursion

When a subroutine calls itself with different parameters

Disadvantages of Iteration

Algorithm may be more difficult to follow/trace because variables are being reused. Need to be careful to get conditions of loops correct. Humans often express the problem in a recursive way (rather than an iterative way)

Advantages of SELECT over IF

All the alternatives depend on the value of one variable. So this makes the code clearer and easier to read/write. Allows multiple branches and avoids nested Ifs. Avoids numerous repeats of similar conditions

Advantage of Recursion

Can be easier to program or more intuitive with an inherently recursive algorithm

Iteration

Code is executed repeatedly for a given number of time or until a condition is met.

Count Controlled Loop (FOR)

FOR loop is set up with a fixed number of iterations. Uses a loop variable e.g. FOR Count = 1 TO 10 ......NEXT Count

Condition Controlled Loop (REPEAT UNTIL)

REPEAT UNTIL loop repeats until some condition become true. E.g. REPEAT....UNTIL Count > 10

Disadvantage of Recursion

Uses many sets of variables (one set per call) therefore less efficient use of memory and often slower and can run out of stack space causing run time error.

Advantages of Iteration

Uses only one set of variables so more efficient use of memory and can be faster. Less likely to run out of space

SELECT (CASE)

Value of variable/expression used to determine which statement of options is executed. There can be a default option

Condition Controlled Loop (WHILE)

WHILE loops run repeatedly depending on a condition (it repeats while the condition is true. E.g. WHILE Count < 11.....END WHILE