Programming Selection Control Structures

Selection Control Structures

• Programs use control structures to control program flow.
• Three types: sequential, selection, and repetition.

Sequential Control

• A series of statements executed one after another.
• Statements are executed in the order they appear.

Selection Control

• Used to execute one set of statements if a condition is TRUE, a different set if FALSE, or no statements at all.
• The program's flow depends on whether a condition is true or false.

Repetition Control

• Used to execute a set of statements repeatedly as long as a given condition is TRUE.
• The program keeps looping as long as the condition is true.

Learning Outcomes

• Students should be able to explain selection control structures.
• Students should be able to use relational and logical operators.
• Students should be able to use if, if...else, if...else if, switch...case, nested if statements, and conditional operators.

Why Selection

• Selection allows a program to choose an action based on a condition.
• For example, password checks control user access.
• Conditions need to be TRUE or FALSE.

Boolean Values

• Boolean expressions are used for conditions.
• TRUE is assigned 1; FALSE is 0.

Boolean Expressions

• Relational operators make comparisons.
• Logical operators combine relational expressions.
• Relational and logical expressions are boolean expressions.

Relational Operators

• Used to compare two values.
• Examples: <, <=, >, >=, ==, !=
• Examples using ints y = 6, x = 5 (y>x, T; y<2, F; x>=3, T; y<=x, F; x ==5, T; y !=6, F)

Logical Operators

• Used to combine two or more relational expressions.
• Examples: && (AND), || (OR), ! (NOT)
• Truth table examples given for AND, OR, NOT operations

Operator Precedence

• Arithmetic operators have higher precedence than relational ones, which are higher than logical ones.
• Parentheses can be used to control order of operations.
• Examples are provided for precedence in calculating expressions.

Boolean Expressions in Variables

• Boolean expressions can be assigned to variables.
• 0 means FALSE; any other value means TRUE.

Checking Numeric Ranges

• Used to test if a value is within a range (e.g., a valid grade).
• Cannot use mathematical notation like 0 <= grade <= 100;

if Statement

• Used for a single selection path.
• Statements following condition execute conditionally.

if...else Statement

• Used to create a two-way selection path.
• One statement block for TRUE condition; another block for FALSE condition.

if...else if Statement

• Used to create a multiple-path selection.
• Statements are executed sequentially based on testing conditions.

Nested if Statements

• One if statement inside another if or else statement.

Dangling else

• The else is associated with the closest unmatched if

Switch...Case Statement

• Used for multiple selection paths.
• Each case corresponds to a possible value.
• A default case is for unexpected input.
• Requires cases to compare against a single value, (e.g., a number, or a choice represented by a letter)

Menu-Driven Programs

• Programs with menus of choices for the user.
• Program execution is controlled by what the user selects from the menu.

Example Code

• Various example code snippets illustrating use of different types of selection statements.