Activity 2.2 If Statements

Introduction

Activity 2.2

If Statements

Topics

Making Decisions
If Statements
Common Mistakes when Writing If Statements

Making Decisions

Programs often need to make choices. As discussed in the previous lesson, a program often needs to decide what to do based on certain circumstances.

This kind of decision-making is called selection. It lets your program follow different paths depending on what's true.

The `if` Statement

An if statement allows your program to check a condition and decide whether or not to execute a block of code based on whether its condition is true or false.

1
System.out.print("Enter your age: ");
2
int age = input.nextInt();
3

4
if (age >= 16) {
5
  System.out.println("You can drive!");
6
}

Components of an `if` Statement

1
if (age >= 16) {
2
  System.out.println("You can drive!");
3
}

1. (if) If keyword - Denotes the beginning of an if statement.

2. (age >= 16) Condition - A boolean expression that evaluates true or false.

3. ({ }) Code Block: A group of statements surrounded by braces.

Demo: Create the Driving Age Checker

1
System.out.print("Enter your age: ");
2
int age = input.nextInt();
3

4
if (age >= 16) {
5
  System.out.println("You can drive!");
6
}

1
Enter your age: 17 [Enter]
2
You can drive!

1
Enter your age: 12 [Enter]
2
[No output]

Common Mistakes

1. Forgetting to Close a Code Block: Always let your editor generate the closing brace and avoid deleting it. New programmers often forget to close their code blocks.

2. Poor indentation: Indent all code within a block by one tab. While not required by the compiler, this makes your code much easier to read and maintain.

3. Unnecessary semi-colons: if (condition); { Avoid placing semi-colons after an if statement's condition. A semi-colon here separates the condition from the code block, causing the block to run unconditionally.

Key Terms

Selection: The ability of a program to choose which code to execute based on a condition.
if Statement: A fundamental control flow structure that allows a program to execute a block of code only if a specified condition is true. It consists of the if keyword, a condition, and a code block.

Key Terms

Condition: A logical expression that evaluates to a Boolean value (true or false). It determines whether the code inside an if statement's code block will be executed.
Code Block: A group of one or more programming statements enclosed in curly braces ({ }). In an if statement, this block of code is executed when the condition is met.

'F' → Fullscreen

Objectives

Constructing If Statements
Evaluating Conditions
Grouping code into code blocks

Activity Tasks

Create a new project named 2-2-If-Statements.
Complete each task individually.

Task 1: Age Validator

1
import java.util.Scanner;
2

3
public class Program {
4
    public static void main(String[] args) {
5
        Scanner input = new Scanner(System.in);
6

7
        System.out.println("--- Demo 1 - Age Validator ---");
8

9
        System.out.print("Enter your age: ");
10
        int userAge = input.nextInt();
11

12
        input.nextLine(); // Consume newline
13

14
        if (userAge >= 16) {
15
            System.out.println("Time to hit the road! You've earned your driving permit.\n");
16
        }
17

18
        if (userAge >= 18) {
19
            System.out.println("Adulting 101: You can now vote and live independently.");
20
            System.out.println("Please exit your mom's basement.\n");
21
        }
22

23
        if (userAge >= 35) {
24
            System.out.println("You're old enough to run for president.");
25

26
            System.out.print("Enter your full name: ");
27
            String fullName = input.nextLine();
28

29
            System.out.print("What year will you run? ");
30
            String electionYear = input.nextLine();
31

32
            System.out.print("What's your nickname (e.g., 'The Awesome')? ");
33
            String nickName = input.nextLine();
34

35
            System.out.println(nickName + " " + fullName + " for president in " + electionYear + "!");
36
        }
37

38
        System.out.println("Press enter to continue...");
39
        input.nextLine();
40
        // -----------------------------------------------------------------------------
41
//
42
    }
43
}

Task 2: Simple Score Calculator

1
import java.util.Scanner;
2

3
public class Program {
4
    public static void main(String[] args) {
36 collapsed lines
5
        Scanner input = new Scanner(System.in);
6

7
        System.out.println("--- Demo 1 - Age Validator ---");
8

9
        System.out.print("Enter your age: ");
10
        int userAge = input.nextInt();
11

12
        input.nextLine(); // Consume newline
13

14
        if (userAge >= 16) {
15
            System.out.println("Time to hit the road! You've earned your driving permit.\n");
16
        }
17

18
        if (userAge >= 18) {
19
            System.out.println("Adulting 101: You can now vote and live independently.");
20
            System.out.println("Please exit your mom's basement.\n");
21
        }
22

23
        if (userAge >= 35) {
24
            System.out.println("You're old enough to run for president.");
25

26
            System.out.print("Enter your full name: ");
27
            String fullName = input.nextLine();
28

29
            System.out.print("What year will you run? ");
30
            String electionYear = input.nextLine();
31

32
            System.out.print("What's your nickname (e.g., 'The Awesome')? ");
33
            String nickName = input.nextLine();
34

35
            System.out.println(nickName + " " + fullName + " for president in " + electionYear + "!");
36
        }
37

38
        System.out.println("Press enter to continue...");
39
        input.nextLine();
40
        // -----------------------------------------------------------------------------
41

42
        System.out.println("\n--- Demo 2 - Simple Score Calculator ---");
43

44
        System.out.print("Enter your score (0-100): ");
45
        int score = input.nextInt();
46

47
        input.nextLine(); // Consume newline
48

49
        if (score >= 60) {
50
            System.out.println("You passed!");
51
        }
52

53
        if (score < 60) {
54
            System.out.println("You did not pass. Keep studying!");
55
        }
56

57
        System.out.println("Press enter to continue...");
58
        input.nextLine();
59
        // -----------------------------------------------------------------------------
60
//
61
    }
62
}

Task 3: Temperature Check

1
import java.util.Scanner;
2

3
public class Program {
4
    public static void main(String[] args) {
55 collapsed lines
5
        Scanner input = new Scanner(System.in);
6

7
        System.out.println("--- Demo 1 - Age Validator ---");
8

9
        System.out.print("Enter your age: ");
10
        int userAge = input.nextInt();
11

12
        input.nextLine(); // Consume newline
13

14
        if (userAge >= 16) {
15
            System.out.println("Time to hit the road! You've earned your driving permit.\n");
16
        }
17

18
        if (userAge >= 18) {
19
            System.out.println("Adulting 101: You can now vote and live independently.");
20
            System.out.println("Please exit your mom's basement.\n");
21
        }
22

23
        if (userAge >= 35) {
24
            System.out.println("You're old enough to run for president.");
25

26
            System.out.print("Enter your full name: ");
27
            String fullName = input.nextLine();
28

29
            System.out.print("What year will you run? ");
30
            String electionYear = input.nextLine();
31

32
            System.out.print("What's your nickname (e.g., 'The Awesome')? ");
33
            String nickName = input.nextLine();
34

35
            System.out.println(nickName + " " + fullName + " for president in " + electionYear + "!");
36
        }
37

38
        System.out.println("Press enter to continue...");
39
        input.nextLine();
40
        // -----------------------------------------------------------------------------
41

42
        System.out.println("\n--- Demo 2 - Simple Score Calculator ---");
43

44
        System.out.print("Enter your score (0-100): ");
45
        int score = input.nextInt();
46

47
        input.nextLine(); // Consume newline
48

49
        if (score >= 60) {
50
            System.out.println("You passed!");
51
        }
52

53
        if (score < 60) {
54
            System.out.println("You did not pass. Keep studying!");
55
        }
56

57
        System.out.println("Press enter to continue...");
58
        input.nextLine();
59
        // -----------------------------------------------------------------------------
60

61
        System.out.println("\n--- Demo 3 - Temperature Check ---");
62

63
        System.out.print("What is the current temperature in Fahrenheit? ");
64
        int currentTemp = input.nextInt();
65

66
        input.nextLine(); // Consume newline
67

68
        if (currentTemp <= 32) {
69
            System.out.println("Brrr! It's freezing. Don't forget your coat!");
70
        }
71

72
        if (currentTemp > 32 && currentTemp <= 65) {
73
            System.out.println("It's a bit chilly. A light jacket should be perfect.");
74
        }
75

76
        if (currentTemp > 65) {
77
            System.out.println("It's warm outside. Enjoy the nice weather!");
78
        }
79

80
        System.out.println("Press enter to continue...");
81
        input.nextLine();
82
        // -----------------------------------------------------------------------------
83
//
84
    }
85
}

Task 4: Letter Grade Calculator

1
import java.util.Scanner;
2

3
public class Program {
4
    public static void main(String[] args) {
78 collapsed lines
5
        Scanner input = new Scanner(System.in);
6

7
        System.out.println("--- Demo 1 - Age Validator ---");
8

9
        System.out.print("Enter your age: ");
10
        int userAge = input.nextInt();
11

12
        input.nextLine(); // Consume newline
13

14
        if (userAge >= 16) {
15
            System.out.println("Time to hit the road! You've earned your driving permit.\n");
16
        }
17

18
        if (userAge >= 18) {
19
            System.out.println("Adulting 101: You can now vote and live independently.");
20
            System.out.println("Please exit your mom's basement.\n");
21
        }
22

23
        if (userAge >= 35) {
24
            System.out.println("You're old enough to run for president.");
25

26
            System.out.print("Enter your full name: ");
27
            String fullName = input.nextLine();
28

29
            System.out.print("What year will you run? ");
30
            String electionYear = input.nextLine();
31

32
            System.out.print("What's your nickname (e.g., 'The Awesome')? ");
33
            String nickName = input.nextLine();
34

35
            System.out.println(nickName + " " + fullName + " for president in " + electionYear + "!");
36
        }
37

38
        System.out.println("Press enter to continue...");
39
        input.nextLine();
40
        // -----------------------------------------------------------------------------
41

42
        System.out.println("\n--- Demo 2 - Simple Score Calculator ---");
43

44
        System.out.print("Enter your score (0-100): ");
45
        int score = input.nextInt();
46

47
        input.nextLine(); // Consume newline
48

49
        if (score >= 60) {
50
            System.out.println("You passed!");
51
        }
52

53
        if (score < 60) {
54
            System.out.println("You did not pass. Keep studying!");
55
        }
56

57
        System.out.println("Press enter to continue...");
58
        input.nextLine();
59
        // -----------------------------------------------------------------------------
60

61
        System.out.println("\n--- Demo 3 - Temperature Check ---");
62

63
        System.out.print("What is the current temperature in Fahrenheit? ");
64
        int currentTemp = input.nextInt();
65

66
        input.nextLine(); // Consume newline
67

68
        if (currentTemp <= 32) {
69
            System.out.println("Brrr! It's freezing. Don't forget your coat!");
70
        }
71

72
        if (currentTemp > 32 && currentTemp <= 65) {
73
            System.out.println("It's a bit chilly. A light jacket should be perfect.");
74
        }
75

76
        if (currentTemp > 65) {
77
            System.out.println("It's warm outside. Enjoy the nice weather!");
78
        }
79

80
        System.out.println("Press enter to continue...");
81
        input.nextLine();
82
        // -----------------------------------------------------------------------------
83

84
        System.out.println("\n--- Demo 4 - Letter Grade Calculator ---");
85

86
        System.out.print("Enter your final grade percentage (0-100): ");
87
        int finalGrade = input.nextInt();
88

89
        if (finalGrade >= 90) {
90
            System.out.println("You got an A! Excellent work!");
91
        }
92

93
        if (finalGrade >= 80 && finalGrade < 90) {
94
            System.out.println("You got a B! Great job!");
95
        }
96

97
        if (finalGrade >= 70 && finalGrade < 80) {
98
            System.out.println("You got a C. Solid effort.");
99
        }
100

101
        if (finalGrade >= 60 && finalGrade < 70) {
102
            System.out.println("You got a D. You passed, but there's room to improve.");
103
        }
104

105
        if (finalGrade < 60) {
106
            System.out.println("You got an F. Let's review the material and try again.");
107
        }
108
//
109
    }
110
}

Sample Output

Your program output should something similar to the sample output below.

--- Demo 1 - Age Validator ---
Enter your age: 35
Time to hit the road! You've earned your driving permit.

Adulting 101: You can now vote and live independently.
Please exit your mom's basement.

You're old enough to run for president.
Enter your full name: Anthony Mortimer
What year will you run? 2028
What's your nickname (e.g., 'The Awesome')? Sleepy
Sleepy Anthony Mortimer for president in 2028!
Press enter to continue...


--- Demo 2 - Simple Score Calculator ---
Enter your score (0-100): 83
You passed!
Press enter to continue...


--- Demo 3 - Temperature Check ---
What is the current temperature in Fahrenheit? 72
It's warm outside. Enjoy the nice weather!
Press enter to continue...


--- Demo 4 - Letter Grade Calculator ---
Enter your final grade percentage (0-100): 76
You got a C. Solid effort.

Reflection Questions

You may write your reflection answers as comments at the bottom of your code.

Describe a real-life situation where you make a decision based on multiple conditions. How would you translate that decision-making process into an if statement using logical operators like && (AND) and || (OR)?

Submission

Submit your activity and reflection answers to the appropriate dropbox.

Activity 2.2 If Statements

Introduction

Activity 2.2

If Statements

Topics

Making Decisions

The if Statement

Components of an if Statement

Demo: Create the Driving Age Checker

Common Mistakes

Key Terms

Key Terms

Objectives

Activity Tasks

Task 1: Age Validator

Task 2: Simple Score Calculator

Task 3: Temperature Check

Task 4: Letter Grade Calculator

Sample Output

Reflection Questions

Submission

Activity Complete

The `if` Statement

Components of an `if` Statement