Experiments with Taking Decisions using Code (Conditional Statements)

Topics

1. Experiments with Boolean Expressions
2. Experiments of What could go Wrong?

Experiments with Boolean Expressions

1. Check the results of the following (one by one):

    System.out.println( 13 < 35 );
    System.out.println( 13 > 35 );
    System.out.println( 13 <= 35 );
    System.out.println( 13 >= 35 );
    System.out.println( 13 == 35 );
    System.out.println( 13 != 35 );
    System.out.println( (13 < 35) && (13 < 50) );
    System.out.println( (13 < 35) || (13 < 50) );
    System.out.println( !(13 < 35) );
   

   You can copy all the lines and paste in your code. But hide other lines when testing each line. Take note of the condition along with its result.

2. Now, try changing those values and repeat the above experiment. Some ways of the experiment:
   1. Keep the same operator and same left side value, and change the right side value to:
      1. Same value as left value
      2. Lesser value than left value
      3. Bigger value than left value
   2. Hide the line that you just experimented with, unhide the other line and repeat the above experiment.

   Take note of the condition along with its result.

3. Now, declare two variables of any data type except String and read values for them. Repeat the above operations and check results.

4. Take two integers as input and check the relation between them with relational operators. Print the relation in the given format.
   Sample Behavior
   Input:
   37
   13
   Output:
   37 is greater than 13

   Input:
   11
   11
   Output:
   Both are equal

5. Take an integer as input and check if the number is between 1 and 100.
   Hint:
   Use range checking using relational operators and && operator with “if”
6. Take an integer as input and check if the number is NOT in between 1 and 100.
   Hint:
   Use range checking using relational operators and logical operators with “if”
7. Take age as input and print if the person is eligible to vote or not.
   Hint:
   Use “if-else”
8. Take an integer as input, print if that number is positive, negative or zero.
   Hint:
   Use “if-else-if”
9. Print the following menu and ask User to choose any one value. Then based on the value, print something about it.
   Sample Behavior #1:
   1. Breakfast
   2. Lunch
   3. Snacks
   4. Dinner What do you want to eat: 2 We have the following in Lunch: A. South Indian Thali B. North Indian Thali C. Biryani

   Sample Behavior #2:

   1. Breakfast
   2. Lunch
   3. Snacks
   4. Dinner What do you want to eat: 6 Wrong Choice! Please choose a number from Menu.

   Hint: Use any of the following options:

   1. if-else-if
   2. switch

Experiments (What Could Go Wrong - Syntactically, Logically, and Exceptionally)

Experiment 1: Forgetting the else Block

What Could Go Wrong?

• Logically: If you forget to include an else block when it’s needed, certain inputs might not be handled properly, leading to unexpected behavior.

Example:

public class LoginSystem {
    public static void main(String[] args) {
        String storedPassword = "securePass";
        String enteredPassword = "wrongPass";

        if (enteredPassword.equals(storedPassword)) {
            System.out.println("Login successful.");
        }
        // No else block to handle incorrect password
    }
}

What Happens:

• Expected: You might expect a message saying “Login failed” if the password is incorrect.
• Actual: The program will do nothing if the password is incorrect because there’s no else block to handle this case.

Solution:

• Add an else block to handle the case where the passwords don’t match.

if (enteredPassword.equals(storedPassword)) {
    System.out.println("Login successful.");
} else {
    System.out.println("Login failed.");
}

Experiment 2: Misusing else if Instead of Multiple if Statements

What Could Go Wrong?

• Logically: Using else if when you actually need multiple independent if statements can cause only one condition to be checked, ignoring others that might also be true.

Example:

public class HealthCheck {
    public static void main(String[] args) {
        int temperature = 101; // Fever
        int bloodPressure = 140; // High blood pressure

        if (temperature > 100) {
            System.out.println("You have a fever.");
        } else if (bloodPressure > 130) {
            System.out.println("You have high blood pressure.");
        }
    }
}

What Happens:

• Expected: The program should check for both fever and high blood pressure.
• Actual: Only the fever condition is checked because the else if prevents the second condition from being evaluated if the first is true.

Solution:

• Use separate if statements when multiple conditions need to be checked independently.

if (temperature > 100) {
    System.out.println("You have a fever.");
}
if (bloodPressure > 130) {
    System.out.println("You have high blood pressure.");
}

Experiment 3: Missing break in a switch Statement

What Could Go Wrong?

• Syntactically: The code will compile, but it may not behave as expected because of unintended fall-through.
• Logically: Without break statements, multiple cases in a switch statement might be executed, leading to incorrect outputs.

Example:

public class VendingMachine {
    public static void main(String[] args) {
        int itemNumber = 2;

        switch (itemNumber) {
            case 1:
                System.out.println("You selected a soda.");
            case 2:
                System.out.println("You selected a snack.");
            case 3:
                System.out.println("You selected water.");
            default:
                System.out.println("Invalid selection.");
        }
    }
}

What Happens:

• Expected: Only the message for the selected item should be printed.
• Actual: Multiple messages might be printed because there are no break statements to stop the execution after each case.

Solution:

• Always include break statements after each case unless you specifically want the fall-through behavior.

switch (itemNumber) {
    case 1:
        System.out.println("You selected a soda.");
        break;
    case 2:
        System.out.println("You selected a snack.");
        break;
    case 3:
        System.out.println("You selected water.");
        break;
    default:
        System.out.println("Invalid selection.");
        break;
}

Experiment 4: Using == Instead of .equals() for String Comparison

What Could Go Wrong?

• Logically: Using == to compare strings checks if the references are the same, not if the content is the same, leading to incorrect results when comparing user inputs or text.

Example:

public class StringComparison {
    public static void main(String[] args) {
        String correctPassword = "securePass";
        String enteredPassword = new String("securePass");

        if (enteredPassword == correctPassword) {
            System.out.println("Login successful.");
        } else {
            System.out.println("Login failed.");
        }
    }
}

What Happens:

• Expected: You might expect “Login successful” because the content of both strings is the same.
• Actual: “Login failed” might be printed because == compares object references, not the content of the strings.

Solution:

• Use the .equals() method to compare the content of strings.

if (enteredPassword.equals(correctPassword)) {
    System.out.println("Login successful.");
} else {
    System.out.println("Login failed.");
}

Experiment 5: Overlooking the Default Case in a switch Statement

What Could Go Wrong?

• Logically: If a switch statement doesn’t include a default case, certain inputs might not be handled, leading to the program doing nothing or behaving unexpectedly.

Example:

public class DayOfWeek {
    public static void main(String[] args) {
        int day = 8; // Invalid day

        switch (day) {
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            // Other cases omitted for brevity
        }
    }
}

What Happens:

• Expected: You might expect an error message or some feedback for an invalid day.
• Actual: Nothing happens if the day doesn’t match any case because there’s no default case.

Solution:

• Always include a default case in a switch statement to handle unexpected or invalid inputs.

switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    default:
        System.out.println("Invalid day.");
        break;
}

Summary of Experiments:

• Syntactical Issues: Forgetting break in a switch statement, using == instead of .equals() for strings.
• Logical Issues: Misusing else if when if is needed, omitting else blocks when they are necessary, or forgetting the default case in switch.
• Exceptional Scenarios: Ensuring all possible conditions are handled, especially with complex conditional logic.

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