First, the increment ++
It can be made variable by the increment operator on the basis of its own plus one;
For subsequent increment a variable, the value of the original variable will increase immediately from a;
Increment symbol: ++
Increment divided into two types: 1, after ++ (a ++); 2, before ++ (++ a);
Thing in common: A ++ and ++ a variable for the original is no difference, the value of the original variables are incremented by one.
Different points: different values and a ++ a ++ a.
A ++ a value equal to the value of the original variable (the value before the increment).
++ a value equal to the new value increase from the original variable.
Example:
a ++ is based on the original value incremented (a = 20, a ++ = 20);
++ a is based on the self-energizing time after the then incremented (++ a = 22);
increment equivalent to twice a (a = 20 + 1 + 1 = 22);
Why a ++ + ++ a + a = 20 + 22 + 22 = 64
Second, since the reduction - -
By decrementing the variable can be in its own on the basis of a decrease;
Minus symbol from : -
Decrement divided into two types : 1, - - (a -); 2 , pre - - (- a);
The same point : a-- and --a will cause the value of the original variable immediately from minus one;
Differences : different values of a-- and --a.
a- - is the original value of the variable (the value before decrementing);
--a is the new value of the original variable (decrementing value);
Example:
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>JS</title> 6 </head> 7 <body> 8 <script> 9 var a=10,b=20; 10 var c=a++; 11 console.log("a="+a); 12 console.log("c="+c); 13 c=++a; 14 console.log("a="+a); 15 console.log("c="+c); 16 c=b--; 17 console.log("c="+c); 18 console.log("b="+b); 19 c=--b; 20 console.log("c="+c); 21 console.log("b="+b); 22 </script> 23 </body> 24 </html>
