php 基础笔记

zhouandtao

　　/***************************bygarcon1986********************************/
　　<?php// boolean integer float example$action = false;if($action == "show version"){echo "the version is 123".'<br>';}else if($action == false){echo "action is false".'<br>';}else {echo "action is true".'<br>';}//some var_dump exercise ---------- var_dump print the relational information of variablesvar_dump((bool)""); //bool(false)var_dump((bool) 1); //bool(true)var_dump((bool) 0); //bool(false)var_dump((bool) -1); //bool(true)var_dump((bool) -2); //bool(true)var_dump((bool) "foo"); //bool(true)var_dump((bool) 2.3e5); //bool(true)var_dump((bool) array()); //bool(false)var_dump((bool) array(12)); //bool(true)var_dump((bool) "false"); //bool(true)//var_dump$a = 3;$b = "s1";//$c = var_dump($a); // int(3)$d = var_dump($a, $b);var_dump((bool)00190); // bool(true)var_dump(00190); // int(1)$large_number =  2147483647;var_dump($large_number);// output: int(2147483647)$large_number =  2147483648;var_dump($large_number);// output: float(2147483648)// it's true also for hexadecimal specified integers between 2^31 and 2^32-1:var_dump( 0xffffffff );// output: float(4294967295)// this doesn't go for hexadecimal specified integers above 2^32-1:var_dump( 0x100000000 );// output: int(2147483647)$million = 1000000;$large_number =  50000 * $million;var_dump($large_number);// output: float(50000000000)var_dump(25/7);  //output float(3.5714285714286)var_dump((int)(25/7)); // int(3)var_dump((boolean)(25/7));// boolean(true)var_dump(round (25/7)); // float(4)//special conditions Warning:Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.echo (int)((0.1+0.7)*10); // echoes 7!echo (int)((0.26-0.1)*100); //echoes 16?>