Question

Explain the purpose of a function parameter. What's the difference between a parameter and an argument?

Short answer

A function parameter is a variable that acts as a placeholder for data that can be passed to the function. The difference between a parameter and an argument is that a parameter is the placeholder defined by the function, while an argument is the actual value passed to the function when it is called.

Step-by-step solution

Define the purpose of a function parameter

A function parameter is a named variable used in a function to refer to one of the pieces of data provided as input to the function. Parameters allow a function to perform a task on a variety of inputs, making the function more flexible and reusable. When defining a function, the parameters act as placeholders for the values that will be passed to the function when it is called.

Distinguish between a parameter and an argument

A parameter is a variable that is defined by the function that receives a value when the function is called. An argument, on the other hand, is the actual value that is passed to the function when it is invoked. In essence, the parameter is like a parking space, and the argument is the car that occupies the parking space at a given time. The parameters represent the 'slots' or 'placeholders' that will accept input values, while arguments are those actual input values.

Key concepts

Function Definition

In C++, a function definition is like a blueprint for a task you want the code to perform. It specifies the name of the function, the type of data it returns, and optionally, the parameters it takes. Parameters are like inputs to the function, defined inside the parentheses that follow the function name. Imagine a function as a little machine: it takes in raw materials (parameters), does some work, and then produces a finished product (the return value).

For example, a simple function definition for adding two integers might look like:

int add(int a, int b) { return a + b;}

Here, 'add' is the function name, 'int' is the return type, and 'a' and 'b' are parameters that the function will use to perform its calculation.

Function Argument

When you've got your function all set up, it's time to use it in the actual code. To do this, you call the function and pass in some specific values - these are your function arguments. The arguments are like real data that get sent into the function to work with. They’re what you actually give to the function so it can run its task with your specific details.

Continuing with our addition example, when you want to add 5 and 3 using the 'add' function, you would call it like this:

int result = add(5, 3);

In this case, 5 and 3 are the arguments. They're the real numbers you're handing over to the 'add' function to process.

Parameter vs Argument

Parameters and arguments are often used interchangeably, but there's a subtle difference between the two. A parameter is like an empty seat in a theater – it's a space reserved for someone, but it doesn't become occupied until a person (the argument) takes the seat. Similarly, in a function, a parameter is the named variable inside the function's definition that will receive a value when the function is called.

Argument, on the other hand, is the actual value that ‘fills’ the parameter’s seat. It’s what you provide when you call a function. Using the earlier 'add' function example:

• Parameter: 'a' and 'b' in the function definition, waiting to receive values.
• Argument: 5 and 3 when you call the function, 'add(5, 3)' providing the actual values.

So, while the terms are related, one represents a sort of 'empty container' waiting to be filled (parameter), and the other the real content that will fill it (argument).