Programming Techniques - Lecture 4: Selection

Programming Techniques - Lecture 4: Selection

• Lecture covers selection statements in programming.
• Key topics include relational operators, logical operators, if statements, if...else statements, conditional operators, nested if statements, if...else if...else statements, switch statements, and how to apply selection in programming.

Relational Operators

• Used to compare numerical values to determine their relative order.
• Operators:
  • Greater than (>): 12 > 5 = true
  • Less than (<): 7 < 5 = false
  • Greater than or equal to (>=): 10 >= 10 = true
  • Less than or equal to (<=): 7 <= 10 = true
  • Equal to (==): 5 == 5 = true
  • Not equal to (!=): 8 != 10 = true

Relational Expressions

• Boolean expressions that evaluate to true or false.
• Example:
  • 12 > 5 = true
  • 7 <= 5 = false
• Can be assigned to a variable. For example, result = x <= y;

Logical Operators

• Used to combine relational expressions.
• Operators:
  • AND (&&): True only if both expressions are true.
  • OR (||): True if either expression is true.
  • NOT (!): Reverses the value of an expression.

Logical Operator Precedence

• ! has the highest precedence, followed by & &, then ||.
• Parentheses can be used to explicitly control evaluation order.

if Statement

• Executes a block of code if a condition is true.
• General format:
  • if (expression)
  • statement;

if...else Statement

• Executes one block of code if a condition is true, otherwise executes another.
• General format:
  • if (expression)
  • statement1;
  • else
  • statement2;

Conditional Operator

• Creates a short if/else statement.
• Format:
  • expr ? expr : expr;

Nested if Statement

• An if statement inside another if statement.
• Used to test multiple conditions.
• Proper indentation is crucial to avoid ambiguity.

if...else if...else Statement

• Tests a series of conditions until one is true.
• Avoid nested ifs when possible by using if...else if... else.
• This is often simpler and allows for cleaner code.

switch Statement

• Selects among multiple statements based on the value of an integer expression.
• Format (using break statements is good practice):
  • switch (expression)
  • `{
    • case exp1: statement1; break;
    • case exp2: statement2; break;
    • ...
    • default: statementn+1;
  • }`

Applying Selection

• Used for input validation, error handling, checking input ranges, creating menus, validating user input comparing character values and comparing strings.

This quiz focuses on selection statements in programming, covering key concepts such as relational and logical operators, if statements, and switch statements. It provides an in-depth look at how selection control structures operate within coding to manage the flow of a program.