Questions about new php students (closed on weekends)

Questions about new php students (closed on weekends) Echo (int) (0.1 + 0.7) * 10); // Display 7
Echo (int) (0.2 + 0.7) * 10); // Display 9
?>
Why is the first execution result not 8?

Reply to discussion (solution)

Floating point number accuracy

 printf('%0.16f',  (0.1+0.7) * 10 ); // 7.9999999999999991

Floating point number accuracy

 printf('%0.16f',  (0.1+0.7) * 10 ); // 7.9999999999999991

Without int, it is 8.
Echo (0.1 + 0.7) * 10); // Display 8

Echo (int) (0.1 + 0.7) * 10); // Display 7
In my understanding, the result in the right parenthesis is forcibly converted to the int type, that is, echo (int) 8;

That's what you got wrong.
(Int) is forcibly converted to an integer. at this time, only the fractional part is truncated and no other processing is performed.
Echo (int) 2.2; // 2
Echo (int) 2.9; // 2
Likewise
Echo (int) 7.9999999999999991; // 7

Echo (0.1 + 0.7) * 10; // 8
This is because php handles the rules based on valid numbers.

Float ?? Accuracy ??.
Http://segmentfault.com/q/1010000002123613

Problem 1: Resolved
Question 2: How can I debug a php project?

Open the error log.

?? ? Ann? Xdebug

Http://www.cnblogs.com/qiantuwuliang/archive/2011/01/23/1942382.html

Class A {function foo () {if (isset ($ this) {// $ this here refers to the class object? Echo '$ this is defined ('; echo get_class ($ this); echo ") \ n";} else {echo "\ $ this is not defined. \ n ";}}$ a = new A (); $ a-> foo (); // Output $ this is defined (A) echo'
'; A: foo (); // $ this is not defined

A: foo () and $ a-> foo () call the same method. why is the output different?

$ This is the instantiated object.

A: foo (); the class method is called statically.
Php 5.3 and later will have a Strict Standards-level error warning:
Non-static method A: foo () shocould not be called statically
Non-static methods cannot be called in static mode

Since you are a beginner, we recommend that you use php 5.4 or later, and the error check level is all
This makes it easy to form good habits.

$ This is the instantiated object.

A: foo (); the class method is called statically.
Php 5.3 and later will have a Strict Standards-level error warning:
Non-static method A: foo () shocould not be called statically
Non-static methods cannot be called in static mode

Since you are a beginner, we recommend that you use php 5.4 or later, and the error check level is all
This makes it easy to form good habits.

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