Intro to Built-in PHP Functions
Number Functions

Another common task in programming is working with numbers, so it shouldn’t surprise us that PHP comes with some handy built-in functions for working with numbers.

The abs() function returns the absolute value of its number argument:

echo abs(-10.99); // Prints: 10.99 echo abs(127); // Prints: 127

Another useful function is the round() function which returns the nearest integer to its number argument:

echo round(1.2); // Prints 1 echo round(1.5); //Prints 2 echo round(1298736.821763876); // Prints: 1298737

Let’s practice!



You’re going to write a function which uses the abs() built-in function within its definition.

Write a function called calculateDistance() that calculates the distance between two numbers. The function should return the same result for two arguments no matter what order they’re passed into the function.

Here are some examples of how the function should work:

  • calculateDistance(-1, 4) should return 5
  • calculateDistance(4, -1) should return 5
  • calculateDistance(3, 7) should return 4
  • calculateDistance(7, 3) should return 4

Once you’ve finished writing your function, you should run it to make sure it’s working how it should.

Check out the hint if you want some help on the strategy or a reminder about how to define your own functions.


Awesome! This time you’re going to write a function which uses the round() function.

Write a function calculateTip() which takes a number representing the total cost of a meal as its argument.

Your function should calculate a new total with an 18% tip added and return that value rounded to the nearest integer.

You’re function must invoke the built-in round() function. For example:

  • calculateTip(100) should return 118
  • calculateTip(35) should return 41
  • calculateTip(88.77) should return 105
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