Lecture 8 · 100 min

Many-Way Decisions

What does a program do when a question has more than two answers?

Teacher view

By the end of this lecture you will be able to

Write an else-if chain and put its conditions in the right order
Use nested conditions and tell which if each else belongs to
Write switch with int, char and String, and control break and default
Choose between if, switch and the ternary operator to suit the problem
Build complete programs: a menu calculator, days in a month, leap years and a cash machine

In this lecture

Many questions have more than two answers
A chain runs the first branch whose condition is true, then skips the rest
The order of conditions changes the result: start with the narrowest
The word else is what ties conditions into one chain
A final else guarantees the variable gets a value
A nested if asks its question only after an earlier one succeeds
else matches the nearest open if before it, whatever the indentation says
Leap years: one rule that combines three conditions
switch jumps to the case equal to the value
Without break the program carries on into the next cases
Deliberate fall-through groups several cases into one answer
switch also works with char and String
Use switch for exact values, and if for everything else
The ternary operator picks between two values in one expression
Final exercise: a menu calculator that brings it all together
Review questions

Part one: else-if chains

Many questions have more than two answers

if-else chooses between only two roads. But a mark can mean A, B, C, D or F, and a lift button can mean any floor.

else-if chain

Questions in a row about ranges of values: is the mark 90 or more? If not, is it 80 or more?

Nested if

A question inside a question: is the code correct? If it is, is the balance enough?

switch

One question with exact values: which option did you press on the menu?

A chain runs the first branch whose condition is true, then skips the rest

Three answers from two conditions

Press "Debug line by line" and watch the conditions being checked from the top. Then try n = 5 and n = 0. Why does the last else need no condition?

public class Sign {
    public static void main(String[] args) {
        int n = -4;
        if (n > 0) {
            System.out.println("Positive");
        } else if (n < 0) {
            System.out.println("Negative");
        } else {
            System.out.println("Zero");
        }
    }
}

Output

Negative

The temperature is 25. More than one condition is true, so what does the program print?

public class Weather {
    public static void main(String[] args) {
        int temp = 25;
        if (temp > 30) {
            System.out.println("Hot");
        } else if (temp > 20) {
            System.out.println("Warm");
        } else if (temp > 10) {
            System.out.println("Mild");
        } else {
            System.out.println("Cold");
        }
    }
}

Show the output

Output

Warm

Why? temp > 10 is true too, but it is never even checked. As soon as the chain finds a true condition, it runs that branch and leaves.

The grade calculator

Enter 85, then 90, then 89. Notice the second condition needs no mark < 90: with a mark of 90 or more, the program would never reach it.

import java.util.Scanner;

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

The order of conditions changes the result: start with the narrowest

An excellent mark, 95, but the conditions are in reverse order. What does it print?

public class WrongOrder {
    public static void main(String[] args) {
        int mark = 95;
        if (mark >= 60) {
            System.out.println("D");
        } else if (mark >= 70) {
            System.out.println("C");
        } else if (mark >= 80) {
            System.out.println("B");
        } else if (mark >= 90) {
            System.out.println("A");
        } else {
            System.out.println("F");
        }
    }
}

Show the output

Output

Why? 95 is more than 60, so the first condition is true and the chain ends. The program can never reach A, whatever the mark: every mark of 90 or more stops at the first condition. The compiler cannot catch this, because it is a logic error, not a writing error.

The correct grade calculator

Read a whole-number mark from 0 to 100, then print the grade: A from 90 up, B from 80, C from 70, D from 60 and F below that. Do not print a prompt.

import java.util.Scanner;

public class GradeCalculator {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        // Read the mark, then write the chain from highest to lowest

    }
}

stdin

Expected output

Hint 1

Start with the condition mark >= 90, then work your way down.

Hint 2

The last branch is else with no condition, and it prints F.

Solution

import java.util.Scanner;

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

The word else is what ties conditions into one chain

We removed the word `else` between the statements. What does the program print?

public class SeparateIfs {
    public static void main(String[] args) {
        int mark = 85;
        if (mark >= 90) {
            System.out.println("A");
        }
        if (mark >= 80) {
            System.out.println("B");
        }
        if (mark >= 70) {
            System.out.println("C");
        } else {
            System.out.println("F");
        }
    }
}

Show the output

Output

B
C

Why? These are three independent decisions, each checked regardless of the ones before. The last else belongs only to the if right before it, not to all the conditions.

When do you use several separate `if` statements instead of a chain?

A final else guarantees the variable gets a value

The compiler does not read logic

We know one of the two conditions is always true, but the compiler does not. Change the last branch to reassure it.

public class Result {
    public static void main(String[] args) {
        int mark = 70;
        String result;
        if (mark >= 60) {
            result = "Pass";
        } else if (mark < 60) {
            result = "Fail";
        }
        System.out.println(result);
    }
}

Compiler messagemight not have been initialized

Show the fix

public class Result {
    public static void main(String[] args) {
        int mark = 70;
        String result;
        if (mark >= 60) {
            result = "Pass";
        } else {
            result = "Fail";
        }
        System.out.println(result);
    }
}

Output

Pass

Why? The compiler does not weigh what the two conditions mean, so it sees a possible path where result gets no value. An else covers everything left, so no path remains without an assignment.

Part two: nested conditions

A nested if asks its question only after an earlier one succeeds

Cash machine: the code first, then the balance

Press "Debug line by line". Then change pin to 1111, then put it back and change amount to 500. Each wrong answer gets its own message, which one condition with && cannot give.

public class NestedAtm {
    public static void main(String[] args) {
        int pin = 1234;
        int balance = 300;
        int amount = 100;
        if (pin == 1234) {
            if (amount <= balance) {
                balance -= amount;
                System.out.println("Take your cash");
                System.out.println("Balance: " + balance);
            } else {
                System.out.println("Not enough balance");
            }
        } else {
            System.out.println("Wrong code");
        }
    }
}

Output

Take your cash
Balance: 200

A discount that depends on two questions

The purchase is 120 and the customer is a member. Try changing the input to 50 and no, then to 100 and no. Notice printf printing the amount to two decimal places.

import java.util.Scanner;

public class Discount {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double total = input.nextDouble();
        String member = input.next();
        double rate;
        if (total >= 100) {
            if (member.equals("yes")) {
                rate = 0.20;
            } else {
                rate = 0.10;
            }
        } else {
            if (member.equals("yes")) {
                rate = 0.05;
            } else {
                rate = 0.0;
            }
        }
        System.out.printf("Pay: %.2f%n", total - total * rate);
    }
}

Output

Pay: 96.00

Cash machine withdrawal

The balance is a constant, 500. Read the amount to withdraw as a whole number and check in this order: if it is 0 or less print Invalid amount; if it is above the balance print Not enough balance; if it is not a multiple of 10 print Use multiples of 10. Otherwise print two lines: Take <amount>, then Balance: <remaining>. Do not print a prompt.

import java.util.Scanner;

public class Withdraw {
    public static void main(String[] args) {
        final int BALANCE = 500;
        Scanner input = new Scanner(System.in);
        // Read the amount, then check each case in order

    }
}

stdin

Expected output

Take 100
Balance: 400

Hint 1

A multiple leaves no remainder: amount % 10 != 0 means it is not a multiple of 10.

Hint 2

A constant cannot change, so print BALANCE - amount directly.

Solution

import java.util.Scanner;

public class Withdraw {
    public static void main(String[] args) {
        final int BALANCE = 500;
        Scanner input = new Scanner(System.in);
        int amount = input.nextInt();
        if (amount <= 0) {
            System.out.println("Invalid amount");
        } else if (amount > BALANCE) {
            System.out.println("Not enough balance");
        } else if (amount % 10 != 0) {
            System.out.println("Use multiples of 10");
        } else {
            System.out.println("Take " + amount);
            System.out.println("Balance: " + (BALANCE - amount));
        }
    }
}

else matches the nearest open if before it, whatever the indentation says

The `else` looks as if it belongs to the first condition. Does it? `x` is 5.

public class DanglingElse {
    public static void main(String[] args) {
        int x = 5;
        if (x > 0)
            if (x > 10)
                System.out.println("Big");
        else
            System.out.println("Not positive");
        System.out.println("End");
    }
}

Show the output

Output

Not positive
End

Why? The compiler ignores indentation and ties else to the nearest if before it, which is x > 10. 5 is positive but not above 10, so Not positive prints, which plainly means the wrong thing.

Braces settle the matter

The same program, but the braces tie else to the first condition. Press "Debug line by line", then try x = -2 and x = 20.

public class ElseWithBraces {
    public static void main(String[] args) {
        int x = 5;
        if (x > 0) {
            if (x > 10) {
                System.out.println("Big");
            }
        } else {
            System.out.println("Not positive");
        }
        System.out.println("End");
    }
}

Output

End

In the code above without braces: which `if` does `else` go with?

Leap years: one rule that combines three conditions

Year	Divides by 4?	Divides by 100?	Divides by 400?	Leap?
`2024`	Yes	No	No	Yes
`2023`	No	No	No	No
`1900`	Yes	Yes	No	No
`2000`	Yes	Yes	Yes	Yes

The rule: a year is a leap year if it divides by 4 and not by 100, or if it divides by 400.

Name each part of the condition

Boolean variables with clear names make a long condition readable. Try the four years in the table and follow the values with "Debug line by line".

public class LeapParts {
    public static void main(String[] args) {
        int year = 1900;
        boolean by4 = year % 4 == 0;
        boolean by100 = year % 100 == 0;
        boolean by400 = year % 400 == 0;
        System.out.println(by4);
        System.out.println(by100);
        System.out.println(by400);
        System.out.println((by4 && !by100) || by400);
    }
}

Output

true
true
false
false

Is it a leap year?

Read a year, then print Leap year if it is one, otherwise print Not a leap year. Do not print a prompt.

import java.util.Scanner;

public class LeapYear {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        // Read the year, then apply the rule

    }
}

stdin

Expected output

Leap year

Hint 1

"Divides by 4" means year % 4 == 0.

Hint 2

(year % 4 == 0 && year % 100 != 0) || year % 400 == 0, and the parentheses make it clear.

Solution

import java.util.Scanner;

public class LeapYear {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int year = input.nextInt();
        if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
            System.out.println("Leap year");
        } else {
            System.out.println("Not a leap year");
        }
    }
}

Part three: switch and the ternary operator

switch jumps to the case equal to the value

switch (value) {
    case 1:
        // runs when value is 1
        break;      // leave the switch
    case 2:
        // runs when value is 2
        break;
    default:
        // runs when no case matches
}

Each case takes a fixed value and a colon, and the lines after it need no braces.

Name of the day

Day 1 is Sunday. Press "Debug line by line" to see the direct jump to case 3. Then try day = 9 to see default at work.

public class DayName {
    public static void main(String[] args) {
        int day = 3;
        switch (day) {
            case 1:
                System.out.println("Sunday");
                break;
            case 2:
                System.out.println("Monday");
                break;
            case 3:
                System.out.println("Tuesday");
                break;
            case 4:
                System.out.println("Wednesday");
                break;
            case 5:
                System.out.println("Thursday");
                break;
            default:
                System.out.println("Weekend or not a day");
        }
        System.out.println("Done");
    }
}

Output

Tuesday
Done

When does `default` run?

Why? default is like the final else of a chain: it takes everything that did not match. It is optional, but it protects the program from unexpected values.

Without break the program carries on into the next cases

Look carefully at where `break` appears. `n` is 2. What does it print?

public class FallThrough {
    public static void main(String[] args) {
        int n = 2;
        switch (n) {
            case 1:
                System.out.println("One");
            case 2:
                System.out.println("Two");
            case 3:
                System.out.println("Three");
                break;
            case 4:
                System.out.println("Four");
            default:
                System.out.println("Other");
        }
    }
}

Show the output

Output

Two
Three

Why? The program jumps to case 2, then keeps moving down line by line without checking any other case until it hits break. This behaviour is called fall-through.

A wrong price from a missing break

Size 1 costs 5, yet the program prints 10. Press "Debug line by line" and watch price change three times. Then add break where it belongs so the program prints Price: 5.

public class SizePrice {
    public static void main(String[] args) {
        int size = 1;
        int price = 0;
        switch (size) {
            case 1:
                price = 5;
            case 2:
                price = 8;
            case 3:
                price = 10;
                break;
            default:
                price = 0;
        }
        System.out.println("Price: " + price);
    }
}

Output

Price: 10

Deliberate fall-through groups several cases into one answer

Days in the month

Seven months have 31 days. Stack their cases on top of each other, and they all fall to the same line. Press "Debug line by line", then change month to 1, then 2, then 13.

public class DaysInMonth {
    public static void main(String[] args) {
        int month = 4;
        int days;
        switch (month) {
            case 1: case 3: case 5: case 7:
            case 8: case 10: case 12:
                days = 31;
                break;
            case 4: case 6: case 9: case 11:
                days = 30;
                break;
            case 2:
                days = 28;
                break;
            default:
                days = 0;
        }
        System.out.println("Days: " + days);
    }
}

Output

Days: 30

Days in the month, leap years included

Read the month number, then the year. Print only the number of days in that month, with February having 29 days in a leap year. If the month is not from 1 to 12, print Invalid month. Do not print a prompt.

import java.util.Scanner;

public class MonthDays {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int month = input.nextInt();
        int year = input.nextInt();
        // Use switch on month; put the leap-year check under case 2

    }
}

stdin

1
2023

Expected output

Hint 1

Inside case 2: write an if-else using the leap-year rule, then break.

Hint 2

Put the error message in default, and print the number of days inside each case before break.

Solution

import java.util.Scanner;

public class MonthDays {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int month = input.nextInt();
        int year = input.nextInt();
        switch (month) {
            case 1: case 3: case 5: case 7:
            case 8: case 10: case 12:
                System.out.println(31);
                break;
            case 4: case 6: case 9: case 11:
                System.out.println(30);
                break;
            case 2:
                if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
                    System.out.println(29);
                } else {
                    System.out.println(28);
                }
                break;
            default:
                System.out.println("Invalid month");
        }
    }
}

switch also works with char and String

Describing a grade with char

A char value is written inside single quotes. Change grade to 'a', then to 'Z'. Notice how case 'A': case 'a': groups the capital and small letters.

public class GradeWords {
    public static void main(String[] args) {
        char grade = 'B';
        switch (grade) {
            case 'A': case 'a':
                System.out.println("Excellent");
                break;
            case 'B': case 'b':
                System.out.println("Very good");
                break;
            case 'C': case 'c':
                System.out.println("Good");
                break;
            default:
                System.out.println("Unknown grade");
        }
    }
}

Output

Very good

A text command from the user

switch works with String since Java 7, and it compares using equals, so it works with text read by Scanner. Change the input to stop, then to Start.

import java.util.Scanner;

public class Commands {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String command = input.next();
        switch (command) {
            case "start":
                System.out.println("Starting");
                break;
            case "stop":
                System.out.println("Stopping");
                break;
            default:
                System.out.println("Unknown command");
        }
    }
}

Output

Starting

The input is `Yes` with a capital letter. What does it print?

import java.util.Scanner;

public class Confirm {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String reply = input.next();
        switch (reply) {
            case "yes":
                System.out.println("Confirmed");
                break;
            case "no":
                System.out.println("Cancelled");
                break;
            default:
                System.out.println("Please answer yes or no");
        }
    }
}

Show the output

Output

Please answer yes or no

Why? switch on strings compares characters exactly, as equals does, and Yes is not yes.

Ticket price

Read the ticket type as one word and use switch: child costs 5, adult costs 10 and senior costs 7. Print Price: <price>, and for any other word print Unknown ticket. Do not print a prompt.

import java.util.Scanner;

public class Ticket {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String type = input.next();
        // Write the switch here

    }
}

stdin

child

Expected output

Price: 5

Hint 1

Do not forget break after each case, or the program prints several prices.

Hint 2

Strings in a case go inside double quotes: case "child":.

Solution

import java.util.Scanner;

public class Ticket {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String type = input.next();
        switch (type) {
            case "child":
                System.out.println("Price: 5");
                break;
            case "adult":
                System.out.println("Price: 10");
                break;
            case "senior":
                System.out.println("Price: 7");
                break;
            default:
                System.out.println("Unknown ticket");
        }
    }
}

Use switch for exact values, and if for everything else

Situation	Best choice	Why
A number from a menu	`switch`	Exact values of one variable
A grade from a mark	`if`	Ranges, not exact values
An age and a card together	`if`	More than one variable
A `double` temperature	`if`	`switch` does not take `double`
A command character such as `+` or `-`	`switch`	Exact `char` values

A condition where a value belongs

A case does not take a condition, only a fixed value. Rewrite the program with if-else so it prints A.

public class CaseRange {
    public static void main(String[] args) {
        int mark = 95;
        switch (mark) {
            case mark >= 90:
                System.out.println("A");
                break;
            default:
                System.out.println("Not A");
        }
    }
}

Compiler messageincompatible types: boolean cannot be converted to int

Show the fix

public class CaseRange {
    public static void main(String[] args) {
        int mark = 95;
        if (mark >= 90) {
            System.out.println("A");
        } else {
            System.out.println("Not A");
        }
    }
}

Output

Why? switch compares the int value mark with each case value. mark >= 90 is a boolean, so it cannot be compared with an int. That is why the message talks about types. Ranges are the job of if.

Two cases with the same value

The programmer meant the second case to print Friday for number 6. Fix the number.

public class DuplicateCase {
    public static void main(String[] args) {
        int day = 6;
        switch (day) {
            case 5:
                System.out.println("Thursday");
                break;
            case 5:
                System.out.println("Friday");
                break;
            default:
                System.out.println("Other");
        }
    }
}

Compiler messageduplicate case label

Show the fix

public class DuplicateCase {
    public static void main(String[] args) {
        int day = 6;
        switch (day) {
            case 5:
                System.out.println("Thursday");
                break;
            case 6:
                System.out.println("Friday");
                break;
            default:
                System.out.println("Other");
        }
    }
}

Output

Friday

Why? If the compiler allowed two equal cases, nobody could say which one the program jumps to. So every case value must be unique inside a switch.

Which problem does not suit `switch`?

Why? A weight is classified by ranges, and switch matches only exact values. The other problems all have known, countable values.

The ternary operator picks between two values in one expression

result = condition ? valueIfTrue : valueIfFalse;

Read it as: is the condition true? If so, the first value; otherwise, the second.

One line instead of five

Change mark to 45 and predict the output. Then rewrite the third line with if-else and compare the two ways.

public class Ternary {
    public static void main(String[] args) {
        int mark = 72;
        int bonus = mark >= 70 ? 5 : 0;
        String result = mark >= 60 ? "Pass" : "Fail";
        System.out.println(result);
        System.out.println("Bonus: " + bonus);
    }
}

Output

Pass
Bonus: 5

It can go straight inside a print, in parentheses. What does this print?

public class TernaryPrint {
    public static void main(String[] args) {
        int x = 7;
        System.out.println(x + " is " + (x % 2 == 0 ? "even" : "odd"));
        int max = x > 10 ? x : 10;
        System.out.println(max);
    }
}

Show the output

Output

7 is odd
10

Why? 7 divided by 2 leaves 1, so the condition is false and we take "odd". In the second line 7 is not above 10, so we take 10.

Price by age

Read the age, then use the ternary operator to give price the value 5 if the age is under 12, otherwise 10. Print Price: <price>. Do not print a prompt.

import java.util.Scanner;

public class AgePrice {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int age = input.nextInt();
        // int price = ... ? ... : ...;

    }
}

stdin

Expected output

Price: 5

Hint 1

The condition is age < 12, and it comes before the ?.

Solution

import java.util.Scanner;

public class AgePrice {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int age = input.nextInt();
        int price = age < 12 ? 5 : 10;
        System.out.println("Price: " + price);
    }
}

Final exercise: a menu calculator that brings it all together

Print the menuFour lines, exactly as in the exercise text.
Read three valuesThe choice as an int, then the two numbers as double.
Choose with switchOne case for each operation, and default for an invalid choice.
Guard the division with ifInside the division case, check that the second number is not zero.

The calculator

Print these four lines: 1) Add, 2) Subtract, 3) Multiply and 4) Divide. Then read the choice and the two numbers. Print Result: followed by the answer to two decimal places using printf. When dividing by zero print Cannot divide by zero, and for any other choice print Invalid choice.

import java.util.Scanner;

public class MenuCalculator {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("1) Add");
        System.out.println("2) Subtract");
        System.out.println("3) Multiply");
        System.out.println("4) Divide");
        // Read the choice and the two numbers, then use switch

    }
}

stdin

1
5
3

Expected output

1) Add
2) Subtract
3) Multiply
4) Divide
Result: 8.00

Hint 1

Dividing a double by zero does not throw an exception; it gives Infinity, so check for it yourself with if.

Hint 2

System.out.printf("Result: %.2f%n", a + b);, followed by break.

Solution

import java.util.Scanner;

public class MenuCalculator {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("1) Add");
        System.out.println("2) Subtract");
        System.out.println("3) Multiply");
        System.out.println("4) Divide");
        int choice = input.nextInt();
        double a = input.nextDouble();
        double b = input.nextDouble();
        switch (choice) {
            case 1:
                System.out.printf("Result: %.2f%n", a + b);
                break;
            case 2:
                System.out.printf("Result: %.2f%n", a - b);
                break;
            case 3:
                System.out.printf("Result: %.2f%n", a * b);
                break;
            case 4:
                if (b != 0) {
                    System.out.printf("Result: %.2f%n", a / b);
                } else {
                    System.out.println("Cannot divide by zero");
                }
                break;
            default:
                System.out.println("Invalid choice");
        }
    }
}

Review questions

At most how many branches run in an `if`, `else if`, `else` chain?

Why? The chain stops at the first true condition. If it has no else and no condition is true, no branch runs at all.

What happens if you forget `break` in a `case`?

Why? A case is only an entry point. Execution stops only at break or at the end of the switch.

Which type does `switch` not accept in Java 8?

Why? Decimal numbers are approximate, so they do not suit exact matching, and switch does not accept them.

Predict: a chain, then a `switch`, then a ternary.

public class ReviewMixed {
    public static void main(String[] args) {
        int n = 15;
        if (n > 20) {
            System.out.println("High");
        } else if (n > 10) {
            System.out.println("Mid");
        } else {
            System.out.println("Low");
        }
        switch (n % 4) {
            case 3:
                System.out.println("Three");
            case 2:
                System.out.println("Two");
                break;
            default:
                System.out.println("Other");
        }
        System.out.println(n > 10 ? "Yes" : "No");
    }
}

Show the output

Output

Mid
Three
Two
Yes

Why? 15 is above 10 but not above 20, so Mid prints. 15 divided by 4 leaves 3, so the program jumps to case 3 and falls into case 2 up to break. Then the ternary prints Yes.

Many questions have more than two answers

A chain runs the first branch whose condition is true, then skips the rest

Three answers from two conditions

The temperature is 25. More than one condition is true, so what does the program print?

The grade calculator

The order of conditions changes the result: start with the narrowest

An excellent mark, 95, but the conditions are in reverse order. What does it print?

The correct grade calculator

The word else is what ties conditions into one chain

We removed the word else between the statements. What does the program print?

When do you use several separate if statements instead of a chain?

A final else guarantees the variable gets a value

The compiler does not read logic

A nested if asks its question only after an earlier one succeeds

Cash machine: the code first, then the balance

A discount that depends on two questions

Cash machine withdrawal

else matches the nearest open if before it, whatever the indentation says

The else looks as if it belongs to the first condition. Does it? x is 5.

Braces settle the matter

In the code above without braces: which if does else go with?

Leap years: one rule that combines three conditions

Name each part of the condition

Is it a leap year?

switch jumps to the case equal to the value

Name of the day

When does default run?

Without break the program carries on into the next cases

Look carefully at where break appears. n is 2. What does it print?

A wrong price from a missing break

Deliberate fall-through groups several cases into one answer

Days in the month

Days in the month, leap years included

switch also works with char and String

Describing a grade with char

A text command from the user

The input is Yes with a capital letter. What does it print?

Ticket price

Use switch for exact values, and if for everything else

A condition where a value belongs

Two cases with the same value

Which problem does not suit switch?

The ternary operator picks between two values in one expression

One line instead of five

It can go straight inside a print, in parentheses. What does this print?

Price by age

Final exercise: a menu calculator that brings it all together

The calculator

Review questions

At most how many branches run in an if, else if, else chain?

What happens if you forget break in a case?

Which type does switch not accept in Java 8?

Predict: a chain, then a switch, then a ternary.

We removed the word `else` between the statements. What does the program print?

When do you use several separate `if` statements instead of a chain?

The `else` looks as if it belongs to the first condition. Does it? `x` is 5.

In the code above without braces: which `if` does `else` go with?

When does `default` run?

Look carefully at where `break` appears. `n` is 2. What does it print?

The input is `Yes` with a capital letter. What does it print?

Which problem does not suit `switch`?

At most how many branches run in an `if`, `else if`, `else` chain?

What happens if you forget `break` in a `case`?

Which type does `switch` not accept in Java 8?

Predict: a chain, then a `switch`, then a ternary.