PHP echo, print_r (expression), var_dump (expression) difference, print_rvar_dump

PHP echo, print_r (expression), var_dump (expression) difference, print_rvar_dump

All three are php statements with output functions, but print_r (expression), var_dump (expression) is a function, and echo is only a language structure, not a function, so it cannot be part of the expression.
For data types in php 8,

What data classes can be output by echo, print_r, and var_dump in PHP? What are their differences?

Echo 'output A string'; // only strings and numbers can be output.

Print_r-prints easy-to-understand information about variables. Generally, the output array structure is used.

Var_dump-prints information about a variable, which is generally used for printing arrays and objects.

Just use it.

What are the differences between echo (), print (), and print_r () in PHP?

Four methods can output strings. Echo

Print ()

Printf ()

Print_r ()
Echo
Multiple values can be output at a time. Multiple values are separated by commas. Echo is a language construct rather than a real function. Therefore, it cannot be used as part of an expression.

Correct syntax: echo "Hello", "World ";
Syntax error: echo ("Hello", "World ");
Print ()
The print () function prints a value (its parameter). If the string is successfully displayed, true is returned. Otherwise, false is returned. For example, if (! Print ("Hello, World ")){

Die ("you are not listening to me ");

}
Printf ()
Printf () is derived from printf () in C language (). This function outputs formatted strings.
Syntax: printf (format, arg1, arg2, arg ++)
Format specifies the string and how to format the variable;
Parameters such as arg1, arg2, ++ are inserted to the percent sign (%) in the main string. This function is executed step by step. In the first % symbol, insert arg1, at the second % symbol, insert arg2, and so on.
Example :? Php

$ Str = "Hello ";

$ Number = 123;

Printf ("% s world. Day number % u", $ str, $ number );

?>
# Results ======
Hello world. Day number 123

If the % symbol is greater than the arg parameter, you must use a placeholder. After the placeholder is inserted with the % symbol, it consists of numbers and "\ $. See example 3.
Example :? Php

$ Number = 123;

Printf ("With 2 decimals: % 1 \ $. 2fbr/> With no decimals: % 1 \ $ u", $ number );

?>
# Result
With 2 decimals: 123.00
With no decimals: 123

Print_r () and var_dump ()
Print_r () can print strings and numbers, while the Array is displayed in the form of an enclosed key and a list of values, and starts with Array. For example, $ a = array ('name' => 'fred ', 'age' => '15', 'wife' => 'wilm ');

Print_r ($ );
Output: Array

{

[Name] => Fred

[Age] => 15

[Wife] => Wilma

}
The same is true for objects. For example, class P {

Var $ name = 'nat ';

//...

}

$ P = new P;

Print_r ($ p );
Output: Object

{

[Name] => nat

}
But print_r () outputs the Boolean value and the NULL result are meaningless, because both print & quo ...... the remaining full text>