Introduction to OOP: Control Statements

Course Information

• Course Title: Introduction to Object Oriented Programming
• Course Code: CO1105
• Lecturer: Ghaith Al-Tameemi
• Institution: School of Computing and Mathematical Sciences, University of Leicester
• Website: https://le.ac.uk/

Lecture 3: Control Statements

Learning Objectives

• Learn and use basic problem-solving techniques
• Develop algorithms using pseudocode
• Use if and if...else statements
• Use while repetition statements
• Use for and do...while statements
• Use switch statements
• Use continue and break statements
• Use logical operators

Problem Solving (Programming like a Professional)

• Thorough understanding of the problem and a meticulously planned approach is essential before coding
• Familiarize yourself with program-building blocks and proven construction techniques

Algorithms

• Computing problems can be solved by executing a series of actions in a particular order
• An algorithm defines the procedure for solving problems through the actions and their order
• Program control is the mechanism for specifying the order in which statements/actions are executed in a program

Pseudocode

• Pseudocode is an informal language for developing algorithms
• It is similar to natural language
• Pseudocode helps to "think out" a program
• It typically describes the actions, input/output, calculations in a program

Control Structures

• Sequential Execution: Statements are executed sequentially; in the order they appear in the code
• Transfer of Control: Java statements alter the normal execution flow
• Three control structures form all programs
  • Sequence structure
  • Selection structure
  • Repetition structure

Sequence Structure

• Computers typically execute instructions sequentially, from top to bottom, unless directed otherwise
• Activity diagram displays the sequential structure where two calculations are performed

Selection Structure

• Three selection statement types
  • if statement
  • if...else statement
  • switch statement

Repetition Structure

• Three looping statement types
  • while statement
  • for statement
  • do...while statement

if Single-Selection Statement

• Pseudocode example: If student's grade is greater than or equal to 60, print "Passed"
• Java code example: if (studentGrade >= 60) System.out.println("Passed");

if...else Double-Selection Statement

• Pseudocode example: If student's grade is greater than or equal to 60, print "Passed"; otherwise, print "Failed"
• Java code example: if (grade >= 60) System.out.println("Passed"); else System.out.println("Failed");

A More Complex Example

• Demonstrates a multi-level nested if...else structure.

while Repetition Statement

• Repeat an action while a condition remains true.
• Example: While there are more items on a shopping list, purchase and remove the next item

Example of Java's while statement

• Find the first power of 3 larger than 100
• Example code: int product = 3; while (product <= 100) {product = 3 * product; }

Block Scope

• Counters are defined before repetition statements in a block
• Example code: int counter = 0; while (counter < 10) { // do something and increase counter; counter = counter + 1; }

Compound Assignment Operators

• Simplify assignment expressions
• Example: c = c + 3 can be written as c += 3

Increment and Decrement Operators

• Unary increment operator (++) adds 1 to the operand
• Unary decrement operator (-) subtracts 1 from the operand
• Prefix operations change the variable's value before using it in an expression
• Postfix operations change the variable's value after using it

Preincrementing and Predecrementing

• Prefix increment/decrement operators increase/decrease the value of a variable before it's used in an expression
• Example: int b = ++a;

Postincrementing and Postdecrementing

• Postfix increment/decrement operators increase/decrease the value of a variable after it's used in an expression
• Example: int b = a++;

Counter-Controlled Repetition with while statement

• Example code illustrating a counter-controlled while loop

The for Repetition Statement

• Specifies counter-controlled repetition details in a single line
• Example Java code
• Detailed explanation of the for loop structure

The for and while loops

• Equivalence between for and while loops in terms of tasks
• Different scenarios when to use for or while loops

More on for Repetition Statement

• Omitting the increment statements
• Demonstration of the increment operation within the loop body avoiding an explicit increment statement

The do...while Repetition Statement

• Loop body executes at least once before checking the condition
• Example code demonstrating the do...while loop

The switch Multiple-Selection Statement

• Performs different actions based on the value of an expression
• Example code
• Definition of the sequence of case labels and default case (optional) for a switch statement

The break Statement

• Causes immediate exit from looping or switch statement
• Used to escape a loop prematurely

The continue Statement

• Skips the remaining statements in a loop and proceeds to the next iteration
• Example code demonstrating the continue statement

Logical Operators

• Conditional AND (&&/&)
• Conditional OR (||/|)
• Boolean AND (&)
• Boolean inclusive OR (|)
• Exclusive OR (^)
• Logical NOT (!)