How is the difference between false and 0 in php?

In PHP, when the variable is 0, the variable is "equal to" false "at the same time. how can we distinguish between 0 and false? This is useful in some condition statements. This article will give an example. First, check the code. the function of this code is to find whether a character string is opened with a certain word.

In PHP, when the variable is 0, the variable is "equal to" false "at the same time. how can we distinguish between 0 and false? This is useful in some condition statements. This article will give an example.

First, check the code. the function of this code is to find whether a string starts with a word.

The instance code is as follows:

1. $ Title = "Hello world .";
2. $ Keyword = "you ";
3. If (strpos ($ title, $ keyword) = 0 ){
4. Echo "correct ";
5. } Else {
6. Echo "error ";
7. }

Output: correct

It seems that the code is correct? Why is the result incorrect? View The Help Manual. when the strpos () function finds a word in a string, if the word exists, the index position of the word is returned. otherwise, false is returned. then, the code is modified as follows.

The instance code is as follows:

1. If (strpos ($ title, $ keyword) = 0 ){
2. Echo "correct ";
3. } Else if (strpos ($ title, $ keyword) = false ){
4. Echo "error ";
5. }

Output: correct

Why is it wrong? In PHP, when the variable is 0, the variable is "equal to" false "at the same time. how can we distinguish between 0 and false? In fact, it is very easy to modify the code:

The instance code is as follows:

1. If (strpos ($ title, $ keyword) === 0 ){
2. Echo "correct ";
3. } Else if (strpos ($ title, $ keyword) === false ){
4. Echo "error ";
5. }

Output: Error

The instance code is as follows:

2. /*
3. * Test boolean
4. * 0 false
5. */
6. $ Num = 0;
7. $ BTest1 = false;
8. $ BTest2 = true;
9. $ StrTest2 = 'false ';
10. If ($ num = $ bTest1)
11. {
12. Echo ('digits 0 and false are equal '); // Display
13. Echo ("
    ");
14. }
15. If ($ bTest1)
16. {
17. Echo ('never executed
    '); // Not displayed
18. }
19. If (1)
20. {
21. Echo ('will it be executed,
    '); // Execute
22. }
23. If ($ bTest2)
24. {
25. Echo ('I am the boss, I want to execute
    '); // Execute
27. }
28. Else {
29. Echo ('none of them belong to me.
    ');
30. }
31. Echo (false = 0); // 1 indicates equal
32. Echo (true = 1); // Display 1 to indicate equal
33. Function testReturn ()
34. {
35. Echo ('aaaaa ');
36. Return;
37. Return 'bbbbbb ';
38. Echo ('cccccc ');
39. }
40. // Return indicates that the return of the function is not executed until it is executed, and exit is the launch program.
41. Echo testReturn (); // call this function to output 'AAA' 'bbbbbbb'
42. ?>

In many cases, false is equal to 0. when we want to return a value containing 0, for example, we need to pay attention to the number query. we can use ===to determine whether it is completely equal,

PHP has a gettype () function to obtain the variable type. you can use the ===operator (after reading it, there are three equal signs ). the difference between the = operator and the = operator is that the operator compares the values and types of data at the same time.

When different variable types are involved in the termination condition, use = and! = It is very important to check the strong type of operators.