Lesson goal: The if-statement

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In the two lessons (here and here) you learned how to generate true or false answers based on the comparison between numbers. Displaying true or false values to the screen, as in those lessons is just the beginning.

The real power of those answers is when you have the computer make decisions based on them. This is what the if statement is all about: making decisions as to what code to execute, based on the answer to a true/false question. In other words, you can tell the computer to do something only if some condition is true.

The if statement looks like this:

if true/false-question then

Move the mouse over a dotted box for more information.

The default code here (reload page if needed) is a simple math-problem tester. It'll generate a couple of random numbers into variables a and b, and make a math problem out of it. The user is prompted to type in the correct answer. An if statement is used to see if the user has typed the correct answer.

Now you try. Write an if statement that will display **Good job** if the user types the correct answer to the math problem.

Type your code here:

See your results here:

This code will not run as-is. Figure out what "true/false-question" you would put between the if and then words to check if ans (the number typed at the keyboard) is equal to the answer of a+b.

Note: the tonumber( ) function wrapped around the input() function is needed to convert what is typed at the keyboard into a numeric form, so it'll work with the comparison operator ==.

If you figure this, can you then figure out how to add another if statement using the ~= ($\ne$) operator to display **wrong** if the user types the wrong answer? Dismiss.

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Does your code work? Want to run it on your iPhone?

Here's your code:

  1. Use [Control]-[C] (Windows) or [⌘]-[C] (MacOS) to copy your code.

  2. Paste it using [Control]-[V] (Windows) or [⌘]-[V] (MacOS) into this page

  3. Then click the "Use on iPhone" button that you'll see.