What do the formal parameters and actual parameters of php functions mean?

In the previous article, we learned what a function is and how to create a function. For the method of creating a function, please see "php function: How to create a function?" 》. This time we come to understand an important one, which is the parameter. Functions cannot do without parameters. Without parameters, the function will not get the information it wants. Today we will take a closer look at parameters.

Before we introduce it, let us first take a look at what parameters are and have a general understanding of them.

Parameters, also called parameter variables. When we study a problem, we focus on changes in some variables and the relationships between them. One or some of them are called independent variables and the other or others are called dependent variables. If we introduce one or more variables to describe changes in the independent and dependent variables, then the introduced variables are not the variables that must be studied in the current problem. We call these variables parametric variables or parameters.

If the function does not have a parameter list, the tasks performed by the function are fixed, and the user cannot change certain execution behaviors inside the function when calling the function.

If the function has a parameter list, the function can obtain the data values ​​required to execute the function from the outside. That is to say, when the user calls a function, before executing the function body, some data is passed to the function through the function's parameter list, so that when the function executes the function body, it can determine how to execute the function body based on the data passed by the user.

Parameters have two forms, namely formal parameters and actual parameters.

First let’s look at a small case.

<?php
function familyName($fname,$year) {
  echo "$fname Zhang. Born in $year <br>";
}

familyName("Li","1975");
familyName("Hong","1978");
familyName("Tao","1983");
?>

The output result is

Li Zhang. Born in 1975
Hong Zhang. Born in 1978
Tao Zhang. Born in 1983

In this case, we can see that there is a bracket after the function, and there are two letters with $ in the bracket, "$fname" and " $year", these two letters are the formal parameters, and the "Li", "1975" and other letters and numbers in brackets after familyName below are the actual parameters.

Through this example, we also have a general understanding of the actual parameters and formal parameters. Let’s learn more about them in detail.

Formal parameters

Formal parameters are the parameter list in parentheses after the function name when defining a function (referred to as "formal parameters"), just like its name Likewise, the formal parameter itself has no specific value. Because the function body needs to use external parameters, in order for the parameters to be passed in correctly, it needs to be passed through the formal parameters and the data in the function body. The formal parameters are as shown in the figure below.

Actual parameters

The actual parameters are the parameters in brackets after the function name when we call the function (referred to as "actual parameters") Parameter"), actual parameters and formal parameters need to correspond one-to-one in order. It will replace the variable value corresponding to the formal parameter in the function body. The parameter of the function can be a specific value or a variable. The actual parameters are as shown below shown.

Now we have finished studying the actual parameters and formal parameters.

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