Returning data is all well and good, but let’s say you’re visiting NYC and you’ve been told that New Yorkers usually add a 20% tip for restaurants and taxis. It would be really convenient if you could just build a function that accepted different prices as input and figured out how much you should tip.

As it happens, you can do that with parameters. Parameters (sometimes called formal parameters) are variables used in a function’s definition. They act as placeholders for the input values you’ll use during your function call.

parameters vs arguments

In the function below, price is the function’s parameter and it’s a double. It is declared between the parentheses and then used in the body of the function.

double get_tip(double price) { return price * 0.2; }

Then, when you’re ready to use your function, the value you pass to the function is called an argument (also known as an actual parameter). In this case, 15.75 is the argument that is passed to the function:

double tip = get_tip(15.75); // tip would be 3.15



You work with emergency services in Britain and the emergency number just changed:

Yikes! That’s a big change. What if the number changes again?

Let’s build a function that prints out the current emergency number, whatever it is from now on.

Above main(), define a void function get_emergency_number() that accepts one parameter:

  • a string with the name emergency_number

In get_emergency_number(), print out “Dial “ with the emergency_number that was passed into the function.


Call get_emergency_number() in main() to see the number get printed!

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