Exercises: Decision Statements

The following exercises shall be used to practice the knowledge about decision statements to improve the understanding of this concept.

Please do the following exercises. Feel free to discuss your solutions with your neighbours.

Write the things you found out down to share them later with the class.

Exercise 1

public class Exercise {

    public static void main(String[] args) {

        System.out.println("This is printed before the if statement");
         
        if (true) {
            System.out.println("The condition is true.");
        }

        System.out.println("This is printed after the if statement");
    }
}

What do you need to change so that the sentence “The condition is true.” is not printed.

Be creative, and put any kind of expression that evaluates to false that come in your mind.

Exercise 2

public class TallestPerson {

    public static void main(String[] args) {
        int currentHeightInCm = 185;
        int newHeightInCm = 187;        

        if (newHeightInCm > currentHeightInCm) {
            currentHeightInCm = newHeightInCm;
        }

        System.out.println("Right now the tallest person in the group is " + currentHeightInCm + "cm tall!");
    }
}

Look at the program above, which is a part of the program we used to introduce programming in the first lesson to find the height of the tallest person in our group. Change the codeblock above so that the user is asked for the height of the next person.

Hint: use the Scanner to get user input.

Exercise 3

Write a small program, which asks the user for their family name and their gender.

Print the options to the screen.

1 -> male
2 -> female

Depending on the user input, print to the screen:

Hello Lady FAMILY NAME

or:

Hello Mister FAMILY NAME

FAMILY NAME should be replaced by the given name of the user.

The output should look similar to this:

Dear lovely user: Please tell me your family name
Müller
Are you male or female?
1 -> male
2 -> female
2
Hello Lady Müller

Starting point:

public class Greetings {

    public static void main(String[] args) {
   
        // Ask for gender
        // Ask for name
        // Greet the user appropriately
    }
}

Bonus: If you want you can add an option if the user does not want to tell their gender!

Exercise 4

Write a small calculator!

• Ask the user for 2 numbers
• Ask the user for an operation. (Similar to Exercise 3: 1 -> +, 2 -> -, 3 -> *, 4 -> /)
• Execute the operation with the two numbers and print the result to the screen!

The output could look similar to this:

4.2
6.7
Please specify an operation: 
1 -> +
2 -> -
3 -> *
4 -> /
3
Result of 4.2 * 6.7 is 28.14

It is enough if you just print the result without the infotext. The infotext is an additional challenge!

Starting point:

public class SimpleCalculator {

    public static void main(String[] args) {
   
        // Ask the user for the first number
        // Ask the user for the second number
        // Print the operations supported by the calculator
        // Ask the user which operation they want to perform
        // Print the result
    }
}

Exercise 5

Write a small program that

• asks the user to enter a year (e.g. 2012)
• asks the user to enter a month (i.e. a number from 1 to 12)
• and then prints the number of days in the month in the given year

For example, for year 2012 and month 3 it should print 31 (the tricky part is the february)

Starting point:

public class Main {

    public static void main(String[] args) {
   
        // Ask the user for a year
        // Ask the user for a month
        // Print the number of days of the month in the given year
    }
}

Exercise 6

Write a small program that

• asks user for two numbers
• and prints of these two the number that is nearest to 21 without being greater 21
• if both numbers are greater 21, print 0

Examples:
Given 13 and 17, print 17
Given 15 and 22, print 15
Given 23 and 24, print 0