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");
      }
  }