1.6: If Statements

What is logic? You may have heard of someone being logical or reasonable (and maybe unreasonable and illogical!). Logic is the study of reasoning correctly. When we make decisions, do mathematics, or compare and contrast, we reason the best solution based on the scenario. Open the “Logic” menu to see the blocks available. What do you think they do?

The first block in the list is an “if” block. You will be using this block to run different code depending on the condition. You actually use if statements every day!

• If my alarm goes off, then I will wake up. Else, I will stay asleep.
• If I am hungry, I will eat something.
• If it’s sunny out, I will wear sunscreen.
• If my room is clean, I will get my allowance. Else, I will make no money.

The if statement will check if a condition is True or False. The condition attaches to the if block. Let’s try an example. Grab the if statement block and drag it to the workspace.

Now, we are going to compare two values. Grab the comparator block.

From the math menu, choose the “number” block and changes the zeroes to any two numbers you want.

Finally, include a drive command for what Zumi should do if that condition is True.

Run the code! What happens? Now change the code so that the two numbers are the same.

The first time you ran the code, nothing happened. This is because the original condition was False. In the example above, 3 is not equal to 4. That statement is not true, so the drive command will not run. This time, let’s add some code so the program can do something else if the condition was not true. Click on the blue gear and add an else statement.

The else statement will run if the previous condition is not true. Add a message for Zumi to display that the numbers are not equal.

Now when you run the code, if the condition is false, something else will happen instead. Try changing the numbers!

In this next activity, you are going to compare two values X and Y. If X > Y, drive forward. If X < Y, drive in reverse. If neither of these are true, then X and Y must be equal! Write a message on Zumi’s screen, or do a little dance. First, create the variables X and Y and set them to any two values.

Begin with the first case, where X > Y. You will need an if statement, a comparator block, and a drive forward block.

Since there are more than two conditions possible, you are going to add in an else if block underneath the if block. Click on the blue gear and drag an else if block underneath the if block.

For the second case, if X < Y, Zumi should go in reverse.

If there were more cases, you can keep adding as many else if statements that you need. Since there are only three possibilities, if the first two are not True, then by default the program will run the else case, which means the numbers are equal! Click on the blue gear to add the else block. Then, add whatever code you want!

Change the values of the X and Y variables to make the program go through each condition.

In this lesson, you learned how you can compare two values. In the future, you will be able to compare the values of the sensors to make decisions about which direction to drive in or when to stop driving. You will be able to use these if statements in loops to constantly make decisions based on the environment.