Java Conditionals and Loops Lecture Notes

Introduction

• Topics Covered: Conditionals, Loops in Java
• Prerequisites: Input-output, basic processing (e.g., a = a + 1)

Setting Up the Project

• Setup project in IntelliJ IDEA
• Project: Lecture 6 - Conditions and Loops

Conditionals

If Statement

• Syntax: if (boolean expression) { body } else { body }`
  • Example: int salary = 25400; if (salary > 10000) { salary += 2000; } else { salary += 1000; } System.out.println(salary);
• Comments: Multi-line comments: /* comment */

Else If Statement

• Use else if to combine multiple conditions
• Example: if (salary > 20000) { salary += 3000; } else if (salary > 10000) { salary += 2000; } else { salary += 1000; } ``

Loops

Why Use Loops?

• Tasks that repeat multiple times (e.g., print numbers, iterate over data)
• Types of Loops: For loop, While loop, Do-While loop

For Loop

• Syntax: for (initialization; condition; increment/decrement) { body }
  • Example: Printing 1 to 5 for (int num = 1; num <= 5; num++) { System.out.println(num); }
  • Debugging shows step-by-step execution
• Variable Scope: Initialize, check condition, execute body, increment

While Loop

• Syntax: while (condition) { body }
  • Example: Printing 1 to 5 int num = 1; while (num <= 5) { System.out.println(num); num++; }
  • Use when number of iterations is unknown
  • Debugging: Shows how condition is repeatedly checked

Do-While Loop

• Syntax: do { body } while (condition);
  • Example: int num = 1; do { System.out.println(num); num++; } while (num <= 5);
  • Executes at least once, condition checked after body execution

Conditional and Loop Examples

Example 1: Find Largest of Three Numbers

• Method: Use nested if-else int a = 10, b = 20, c = 30; int max = a; if (b > max) max = b; if (c > max) max = c; System.out.println(max);

Example 2: Check Uppercase or Lowercase

• Method: Compare ASCII values char ch = 'A'; if (ch >= 'a' && ch <= 'z') { System.out.println("Lowercase"); } else { System.out.println("Uppercase"); }

Example 3: Fibonacci Sequence

• Method: Use While loop int a = 0, b = 1, n = 7; while (count <= n) { int next = a + b; a = b; b = next; count++; } System.out.println(b);

Example 4: Count Specific Digit in Number

• Method: Use remainder operation int num = 138957; int count = 0; while (num > 0) { int remainder = num % 10; if (remainder == 7) count++; num /= 10; } System.out.println(count);

Example 5: Reverse a Number

• Method: Use remainder operation and multiplication int num = 23597; int result = 0; while (num > 0) { int remainder = num % 10; result = result * 10 + remainder; num /= 10; } System.out.println(result);

Example 6: Basic Calculator Program

• Method: Continuously take input until 'x' is entered while (true) { char op = in.next().charAt(0); if (op == '+' || op == '-' || op == '*' || op == '/' || op == '%') { int num1 = in.nextInt(); int num2 = in.nextInt(); int result; if (op == '+') result = num1 + num2; else if (op == '-') result = num1 - num2; else if (op == '*') result = num1 * num2; else if (op == '/') result = (num2 != 0) ? num1 / num2 : 0; else result = num1 % num2; System.out.println(result); } else if (op == 'x' || op == 'X') { break; } else { System.out.println("Invalid operation"); } }