Unit_3_Selection_Statements_Gaddis

CS102 - Java Programming Language

Conditional (Selection Statement)

• Unit 3 Overview
  • Instructor: Charles Edeki

Objectives of Unit 3

• Main topics covered:
  • The if Statement
  • The if-else Statement
  • Nested if Statements
  • The if-else-if Statement
  • Logical Operators
  • Comparing String Objects
  • The Conditional Operator
  • The switch Statement

The if Statement

• Definition:
  • Determines whether a section of code executes based on a boolean condition.
• Structure:
  • if (boolean expression is true) execute next statement.

Flowcharts

Visual Representation of if Statements

• Flowchart for a basic if statement:
  • Example: "Is it cold outside?"
  • Decision: Yes → wearCoat();

Block if Statement Flowchart

• Example:
  • Decision: Is it cold outside?
  • Actions: wearCoat(); wearHat(); wearGloves();
  • Note: Curly braces {} block multiple statements.

Relational Operators

• Definition:
  • Used in boolean expressions for comparisons.
• Operators and Meanings:
  • > : greater than
  • < : less than
  • >= : greater than or equal to
  • <= : less than or equal to
  • == : equal to
  • != : not equal to

Boolean Expressions

• Definition:
  • Results in true or false conditions.
• Examples:
  • x > y : Is x greater than y?
  • x < y : Is x less than y?

if Statements and Examples

• Example code:
  • if (x > y) System.out.println("X is greater than Y");
  • More complex usage:
  • if(x != y) { ... }

Programming Style in if Statements

• Tips:
  • Multi-line if statements are still a single statement.
  • Proper structure helps readability.
  • Use indentation and curly braces for clarity.
  • Example:
  • Prefer: if (average > 95) grade = 'A';

Block if Statements

• Definition:
  • Group statements using {}.
• Example:
  • if (expression) { statement1; statement2; }
• Without braces, only the next statement after the condition will execute.

Flags

• Definition:
  • Boolean variable that monitors a condition.
• Example usage of a flag:
  • if (average > 95) highScore = true;

Comparing Characters

• Key Points:
  • Characters stored using Unicode.
  • Can be compared using relational operators.
• Example:
  • if(c < 'Z') System.out.println("A is less than Z");

if-else Statements

• Structure:
  • if (expression) statementOrBlockIfTrue; else statementOrBlockIfFalse;

Nested if Statements

• Definition:
  • An if statement within another.
• Flowchart representation.
• Example code structure showing nested conditions.

if-else Matching

• Reminder:
  • Curly braces make code clearer, especially with matching else statements.

if-else-if Statements

• Structure:
  • if (expression_1) { ... } else if (expression_2) { ... } else { ... }
• Simplifies nested logic.

Logical Operators

Types of Logical Operators

• Logical AND (&&) - Both conditions must be true.
• Logical OR (||) - At least one condition must be true.
• Logical NOT (!) - Reverses the truth value.

The && Operator

• Operands must be boolean expressions.
• Example truth table for &&.

The || Operator

• Operands must be boolean expressions.
• Example truth table for ||.

The ! Operator

• Example usage of NOT with conditional statements.

Short Circuiting

• Behavior of logical operators in evaluation.
  • AND stops evaluating when one operand is false.
  • OR stops evaluating when one operand is true.

Order of Precedence

• Operators precedence hierarchy explained with examples.

Comparing String Objects

• Relational operators cannot be used directly.

Ignoring Case in String Comparisons

• Methods: equalsIgnoreCase and compareToIgnoreCase.

Variable Scope

• Definition of local variable scope.
• Importance of when a variable comes into scope.

The Conditional Operator

Overview

• Ternary operator to simplify if-else statements.
• Syntax and functionality.

The switch Statement

Structure

• Use of ordinal values to branch logic.

The case Statement

• Explanation of break statement and its behavior.

The System.out.printf Method

• Overview and formatted output.
• Examples using format specifiers like %d, %f, and %s.

The String.format Method

• Similar to System.out.printf, but returns formatted strings.