Exercise - Create nested decision logic with if, else if, and else - Training

14 minutes

In the previous unit, you used multiple if statements to implement the rules of a game. However, at the end of the unit, you noticed that more expressive if statements are needed to fix a subtle bug in your code.

In this exercise, you'll use if, else, and else if statements to improve the branching options in your code and fix a logic bug.

Use if and else statements instead of two separate if statements

Instead of performing two checks to display the "You win!" or "Sorry, you lose" message, you'll use the else keyword.

Ensure that your Program.cs code matches the following:

Random dice = new Random();

int roll1 = dice.Next(1, 7);
int roll2 = dice.Next(1, 7);
int roll3 = dice.Next(1, 7);

int total = roll1 + roll2 + roll3;

Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");

if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
{
    Console.WriteLine("You rolled doubles! +2 bonus to total!");
    total += 2;
}

if ((roll1 == roll2) && (roll2 == roll3)) 
{
    Console.WriteLine("You rolled triples! +6 bonus to total!");
    total += 6;
}

if (total >= 15)
{
    Console.WriteLine("You win!");
}

if (total < 15)
{
    Console.WriteLine("Sorry, you lose.");
}

This is the code that you completed in the previous unit.

Take a minute to examine the two if statements at the end of the file:
```
if (total >= 15)
{
    Console.WriteLine("You win!");
}

if (total < 15)
{
    Console.WriteLine("Sorry, you lose.");
}
```
Notice that both if statements compare total with the same numeric value. This is the perfect opportunity to use an else statement.
Update the two if statements as follows:
```
if (total >= 15)
{
    Console.WriteLine("You win!");
}
else 
{
    Console.WriteLine("Sorry, you lose.");
}
```
Here, if total >= 15 is false, then the code block following the else keyword will execute. Since the two outcomes are related opposites, this is a perfect scenario for the else keyword.

Your updated Program.cs file should contain the following code:

Random dice = new Random();

int roll1 = dice.Next(1, 7);
int roll2 = dice.Next(1, 7);
int roll3 = dice.Next(1, 7);

int total = roll1 + roll2 + roll3;

Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");

if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
{
    Console.WriteLine("You rolled doubles!  +2 bonus to total!");
    total += 2;
}

if ((roll1 == roll2) && (roll2 == roll3))
{
    Console.WriteLine("You rolled triples!  +6 bonus to total!");
    total += 6;
}

if (total >= 15)
{
    Console.WriteLine("You win!");
}
else 
{
    Console.WriteLine("Sorry, you lose.");
}

Modify the code to remove the stacking bonus for doubles and triples using nesting

In the previous unit, you saw that a subtle logic bug was introduced into your application. You can fix that issue by nesting your if statements.

Nesting allows you to place code blocks inside of code blocks. In this case, you'll nest an if and else combination (the check for doubles) inside of another if statement (the check for triples) to prevent both bonuses from being awarded.

Modify your code to match the following code listing:

Random dice = new Random();

int roll1 = dice.Next(1, 7);
int roll2 = dice.Next(1, 7);
int roll3 = dice.Next(1, 7);

int total = roll1 + roll2 + roll3;

Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");

if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
{
    if ((roll1 == roll2) && (roll2 == roll3))
    {
        Console.WriteLine("You rolled triples!  +6 bonus to total!");
        total += 6;
    }
    else
    {
        Console.WriteLine("You rolled doubles!  +2 bonus to total!");
        total += 2;
    }
}

if (total >= 15)
{
    Console.WriteLine("You win!");
}
else 
{
    Console.WriteLine("Sorry, you lose.");
}

Take a minute to review the nested if statements.

The goal is to create an inner if-else construct where the two outcomes are related opposites, and then use the opposing outcomes (if/true and else/false) to award the bonus points for triples and doubles. To achieve this goal, you check for doubles in the outer if statement, and then for triples in the inner if statement. This pattern ensures that when the inner check for triples returns false, your else code block can award the points for doubles.

Coming up, you will "hard code" the results of your three rolls in order to test your code logic.
Create a blank code line above the line where total is declared and initialized.
To test for a roll of doubles, enter the following code:
```
roll1 = 6;
roll2 = 6;
roll3 = 5;
```
Hard coding the three roll variables enables you to test the code without having to run the application dozens of times.
On the Visual Studio Code File menu, click Save.
In the EXPLORER panel, to open a Terminal at your TestProject folder location, right-click TestProject, and then select Open in Integrated Terminal.

A Terminal panel should open, and should include a command prompt showing that the Terminal is open to your TestProject folder location.
At the Terminal command prompt, to run your code, type dotnet run and then press Enter.

When your code runs, you should see:
```
Dice roll: 6 + 6 + 5 = 17
You rolled doubles!  +2 bonus to total!
You win!
```
To test for a roll of triples, update your hard-coded roll variables as follows:
```
roll1 = 6;
roll2 = 6;
roll3 = 6;
```
On the Visual Studio Code File menu, click Save.
In the EXPLORER panel, to open a Terminal at your TestProject folder location, right-click TestProject, and then select Open in Integrated Terminal.
At the Terminal command prompt, to run your code, type dotnet run and then press Enter.

When your code runs, you should see:
```
Dice roll: 6 + 6 + 6 = 18
You rolled triples!  +6 bonus to total!
You win!
```

Use if, else, and else if statements to give a prize instead of a win-lose message

To make the game more fun, you can change the game from "win-or-lose" to awarding fictitious prizes for each score. You can offer four prizes. However, the player should win only one prize:

If the player scores greater or equal to 16, they'll win a new car.
If the player scores greater or equal to 10, they'll win a new laptop.
If the player scores exactly 7, they'll win a trip.
Otherwise, the player wins a kitten.

Modify the code from the previous steps to the following code listing:

Random dice = new Random();

int roll1 = dice.Next(1, 7);
int roll2 = dice.Next(1, 7);
int roll3 = dice.Next(1, 7);

int total = roll1 + roll2 + roll3;

Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");

if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
{
    if ((roll1 == roll2) && (roll2 == roll3))
    {
        Console.WriteLine("You rolled triples!  +6 bonus to total!");
        total += 6;
    }
    else
    {
        Console.WriteLine("You rolled doubles!  +2 bonus to total!");
        total += 2;
    }

    Console.WriteLine($"Your total including the bonus: {total}");
}

if (total >= 16)
{
    Console.WriteLine("You win a new car!");
}
else if (total >= 10)
{
    Console.WriteLine("You win a new laptop!");
}
else if (total == 7)
{
    Console.WriteLine("You win a trip for two!");
}
else
{
    Console.WriteLine("You win a kitten!");
}

Take a minute to review the updated if-elseif-else construct.

The if, else if, and else statements allow you to create multiple exclusive conditions as Boolean expressions. In other words, when you only want one outcome to happen, but you have several possible conditions and results, use as many else if statements as you want. If none of the if and else if statements apply, the final else code block will be executed. The else is optional, but it must come last if you choose to include it.
Use the technique of temporarily hard coding the roll variables to test each message.

Recap

The combination of if and else statements allows you to test for one condition, and then perform one of two outcomes. The code block for the if will be run when the Boolean expression is true, and the code block for the else will be run when the Boolean expression is false.
You can nest if statements to narrow down a possible condition. However, you should consider using the if, else if, and else statements instead.
Use else if statements to create multiple exclusive conditions.
An else is optional, but it must always come last when included.

Continue

Exercise - Create nested decision logic with if, else if, and else

Use if and else statements instead of two separate if statements

Modify the code to remove the stacking bonus for doubles and triples using nesting

Use if, else, and else if statements to give a prize instead of a win-lose message

Recap

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