TLDR;

Parameter = a function’s input at the time of defining the function

Argument = a function’s input at the time of calling the function

After writing code for a while, most developers inevitably end up creating functions (or methods/procedures in other languages—though I’ll stick with “function” in this article). Whether to reduce repetitive code and make it more reusable, or to encapsulate and hide implementation logic, functions are essential. And of course, many times when we create a function, we need to accept some kind of input into it.

For example, here’s a function in Dart:

String _generateHelloMessage(String peopleName) {
  return 'Hello $peopleName';
}

In this example, we want to create a String that starts with “Hello” followed by a name that we pass into the function as input through a variable called peopleName, which must be a String. We can also say that peopleName is a Parameter of this function.

What is a Parameter?

A Parameter is the term for a variable that we accept as input to a function when we define or declare the function (function declaration). In more formal terms, a parameter is the input of a function in its function signature.

What is an Argument?

You can probably guess what an Argument is by now. An Argument is the variable (or value) that we pass as input to a function when we call that function. For example:

String _generateHelloMessage(String peopleName) {
  return 'Hello $peopleName';
}

String bobName = 'Bob';
print(_generateHelloMessage(bobName)); // Output: Hello Bob

In this case, the variable bobName is the Argument of the _generateHelloMessage function—in other words, it’s the actual value we send for the function to use. Additionally, Argument has another name: Actual parameter, or the “real” parameter.

Summary

Parameter = a function’s input at the time of defining

Argument = a function’s input at the time of calling

Thanks for reading

📚 Hope you enjoy reading!