Reprinted-php questions

Reprinted-php question 1. write the results of the following code:
$ A = "Hello World! ";
$ B = $;
Print ("\ $ B = $ B
");
Print ('$ a = $
');
?>

$ B = Hello World!
$ A = $
// '\' Is an escape character, blocking the special usage of a single special character that follows
// ''Single quotes, shielding the special meanings of almost all special characters including
// In addition, debug the code in the command line,
It is not output as a line feed ~ If it is in browser, let alone

2. write the following code to output the result:
$ A = "First ";
$ B = & $;
$ C = $;
$ A = "Second ";
Print ("$ a, $ B, $ c
");
?>

Second, Second, First
// $ B is the value assigned by $ a, so the change of $ a is the change of $ B.
// $ C can be seen as a copy after $ a is copied once, so it is irrelevant two variables. Therefore, the change of $ a does not affect $ c.

3. write the following code to output the result:
$ A = 2;
$ B = "1.2SBC3 ";
$ C = "EFG ";
$ Result1 = $ a. $ B;
$ Result2 = $ a * $ B;
$ Result3 = $ a * $ c;
Print ("$ result1, $ result2, $ result3
");
?>

21.2sbc3, 2.4, 0
// $ Result1 is the string connection, btw. if the question is 2. $ B, the system reports an error.
// $ Result2 is the multiplication of numbers. in php, the first character that is not a number is automatically discarded.
// $ Result3 is the multiplication of numbers. different from 2, $ c does not have any numeric characters, so the whole is forcibly converted to numeric, that is, 0, then multiply with $ a = 2 and the final result is 0.

4. the following incorrect variable names are:
A. $ _ test B. $ 2abc C. $ Var D. $ % Var

B

5. statement for ($ k = 0; $ k = 1; $ k ++); and Statement for ($ k = 0; $ k = 1; $ k ++ ); the execution times are:
A. infinite and 0 B. 0 and infinite C. Both are infinite D. Both are 0

A

/**
* Here we will focus on this question. it should be okay to select A here, which is well known.
* The problem is, if the first sentence is changed to for ($ k = 0; $ k = 0; $ k ++), how many times will the loop be executed?
*
* The answer is 0.
*
* The reason is that for (expr A; expr B; expr C) is concerned with the true value of the expression expr B when determining whether to execute the loop body.
* Note! $ K = 0 the value of this expression is 0! Instead of the possible one returned after successful replication!
* Therefore, if the cycle judgment condition of the for loop is always false, the loop body will not be executed ~~~
*
*:)
**/


6. php functions do not support the following functions:
A. variable function name B. variable number of parameters C. passing parameters through reference
D. pass the parameter E through the pointer to implement recursive functions

D

7. Which of the following statements about php classes is false:
A. support single inheritance B. support multiple inheritance C. constructor D. Not Support destructor
E. The $ this pointer must be used to reference member variables.

B multi-inheritance seems to require interfaces

8. locate and correct the errors in the following code:
$ A [0] = "" Ryan;
$ B ["value"] = 785.9;
$ C ["blue"] [0] = "Ada ";
Print ("$ a [0], $ B [" value "], $ c [" blue "] [0]
");
?>

$ A [0] = "Ryan ";
$ B ["value"] = 785.9;
$ C ["blue"] [0] = "Ada ";
Print ("$ a [0]". "$ B [value]". "{$ c [blue] [0]}"."
");
?>

// There is nothing to say about quotation marks
// The key is the $ c [blue] [0] of the last line. if you do not enclose it in curly brackets, the system automatically replaces $ c [blue] with the variable. the problem is that this value does not exist. Therefore, the xxxx [0] after the replacement is complete will no longer exist, so an error will be reported. This is the so-called variable array.


9. write the priority of the following operators in the order from high to low:
And, =,>, + ,~

~ +> = And I guess

10. differences between isset () and empty ()


Isset ()
Test whether the variable exists

Empty ()
Test whether the variable is null

In a language like php that does not strictly define variables
If a variable has never been declared, isset = false | empty = true
If a variable has been declared, but the value is NULL, it is the same as the previous case.
If a variable has been declared but assigned a value of '', isset = true | empty = true
If a variable has been declared and assigned a value normally, isset = true | empty = false

Example as follow:
$ B = NULL;
$ C = '';
$ D = 'str ';
Echo isset ($ a). "a \ n ";
Echo empty ($ a). "B \ n ";
Echo isset ($ B). "c \ n ";
Echo empty ($ B). "d \ n ";
Echo isset ($ c). "e \ n ";
Echo empty ($ c). "f \ n ";
Echo isset ($ d). "g \ n ";
Echo empty ($ d). "h \ n ";
?>

11. use as few statements as possible to verify the input Email address.

Eregi ('^ [_ a-z0-9] + (\. [_ a-z0-9-] +) * @ [a-z0-9] + (\. [a-z0-9-] +) * $ ', $ emailaddress)

12. write an algorithm, sort the following arrays in ascending order, and write the name of the sorting algorithm:
$ ArrVar = array)

Bubble sorting, process omitted

13. write a program that converts the first letter of each word in a text file into a large one and saves it back to the original file.
Tip: convert the first letter of a word in a string to a function of uppercase: string ucwords (string str)



14. write out several methods for accessing the MYSQL database using php and give a brief introduction.

15. write out the PHPSession implementation method. introduce the implementation method that you think is the best, and explain the reasons.
Tip: SessionID transmission method, Session variable storage method, etc.

16. What are the vulnerabilities in PHP?

I am the biggest vulnerability ......


I don't know, right ~~ Haha ~~ I found that conceptual things are quite ambiguous ~~
Write more words slowly ~~~ :)