Conditionals & Logic - Reference Handout

What You'll Learn Today

• How to make decisions in your programs
• Using if/else and switch statements
• Combining conditions with logical operators
• Building a grade calculator

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Conditionals in Java

• if: Runs code if a condition is true
• else if: Checks another condition if the first is false
• else: Runs if none of the above are true

Example:

int score = 85;
if (score >= 90) {
    System.out.println("A");
} else if (score >= 80) {
    System.out.println("B");
} else {
    System.out.println("C or below");
}

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Comparison & Logical Operators

• == (equals), != (not equal), <, >, <=, >=
• && (and), || (or), ! (not)

Example:

int age = 16;
if (age >= 13 && age <= 19) {
    System.out.println("Teenager");
}

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Switch Statements

• Use when you have many possible values for one variable

Example:

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Other day");
}

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Mini-Exercises

1. Write a program to check if a number is positive, negative, or zero
2. Use switch to print the name of the day for a number (1-7)

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Challenge: Grade Calculator

• Ask the user for a score (0-100)
• Print the letter grade (A, B, C, D, F)
• Try both if/else and switch approaches

Example (Starter):

import java.util.Scanner;

public class GradeCalculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter your score: ");
        int score = scanner.nextInt();
        if (score >= 90) {
            System.out.println("A");
        } else if (score >= 80) {
            System.out.println("B");
        } else if (score >= 70) {
            System.out.println("C");
        } else if (score >= 60) {
            System.out.println("D");
        } else {
            System.out.println("F");
        }
    }
}

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Troubleshooting Tips

• Wrong grade: Double-check your conditions
• No output: Make sure your if/else covers all cases
• Switch not working: Remember to use break after each case

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End of Day Checklist

• Used if/else and switch
• Built a grade calculator
• Participated in meeting
• Asked at least one question

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Homework (Optional)

Research Topic: "How do loops work in Java?"

Resource: - https://www.w3schools.com/java/java_loops.asp

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Tomorrow's Preview: Loops

• Repeat actions with for, while, and do-while
• Build a number guessing game