Function, we have introduced it in previous courses. The English name of function is: function, and the explanation of function has another meaning: function.

Function is function. Calling a function is calling a function.

We have also learned about some functions before, such as: is_int, phpinfo(), etc. We have introduced them all and they all have different functions. We won’t repeat it here.

The function is like a dog, it roars wherever it is needed.

Through the previous sentence, we can get several different rules:

1. When you need to use a function, just shout its name
2. Function can Repeatedly shout its name and it will come over. That is to say, the function can be called repeatedly

After we understand, let’s explain the classification of functions. We divide functions into two categories:

1. Custom functions
2. System function