php variable operation

Variable operations are divided according to the return value type:

1. Arithmetic operations: return numeric type (integet/float);

2. Logical operations: return Boolean type (true /false);

3. Character operation: Return string type (string);

Memory points: The return types are all scalars, four basic types.

var_dump(5+10);  //返回integer;
echo &#39;<hr>&#39;;
var_dump(3.14*5*5); //返回float;
echo &#39;<hr>&#39;;
var_dump(100>90); //返回布尔型bool的true
echo &#39;<hr>&#39;;
//&&:如果第一个表达式计算结果为false,整个结果就是false,后面就不会再计算了
var_dump(100>90 && 30 >= 50); //&#39;与&#39;返回false
echo &#39;<hr>&#39;;
//||:二个表达式都会被计算
var_dump(100>90 || 30 >= 50); //&#39;或&#39;返回false
echo &#39;<hr>&#39;;
$siteName = &#39;PHP中文网&#39;;
$course = &#39;php编程技术&#39;;
echo &#39;欢迎来到&#39;.$siteName.&#39;学习&#39;.$course; //字符串连接,返回一个新字符串