What is the difference between the declaration and definition of functions in C++

Today, I would like to talk to you about the difference between the declaration and definition of functions in C++. Many people may not understand it very well. In order to make you understand better, the editor has summarized the following for you. I hope you can get something from this article.

The difference between the declaration of a function and the definition of a function

Declaration: usually in the header file, say to the compiler: here I have a function called function () to let the compiler know that this function exists.

Definition: generally in the source file, specifically the function body is specified in the implementation process of the function.

You can also understand it like this:

First of all, when the program in the following figure is executed, the computer executes from top to bottom.

In other words, if there is no function declaration sentence, when the function is executed to the function call sentence, the computer does not know what fun is, he does not know that there is a specific implementation of this function below.

So, you need to declare and tell the computer that this thing does exist, and it's a function, which is defined below.

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