Selection Statements

• A selection statement provides the means of choosing between two or more paths of execution
• Two general categories:

1. Two-way selectors
2. Multiple-way selectors

Two-Way Selection Statements

• General form:

if control_expression

then clause

else clause

• Design Issues:

1. What is the form and type of the control expression?
2. How are the then and else clauses specified?
3. How should the meaning of nested selectors be specified?

Iterative Statements

• The repeated execution of a statement or compound statement is accomplished either by iteration or recursion
• General design issues for iteration control statements:

1. How is iteration controlled?
2. Where is the control mechanism in the loop?

Iteration Based on Data Structures

• The number of elements in a data structure controls loop iteration
• Control mechanism is a call to an iterator function that returns the next element in some chosen order, if there is one; else loop is terminate
• C’s for can be used to build a user-defined iterator:

  for (p=root; p==NULL; traverse(p)){

…

}

• PHP

1.   current points at one element of the array
2.   next moves current to the next element
3.   reset moves current to the first element

• Java 5.0 (uses for, although it is called foreach)

For arrays and any other class that implements the Iterable interface, e.g., ArrayList

for (String myElement : myList) { … }