0103 increment and decrement operators

Increment and decrement operators Overview

If necessary to repeatedly add or subtract a variable number, you can increment (+) and decrement (-) operator to complete.

在 JavaScript 中，递增（++）和递减（ -- ）既可以放在变量前面，也可以放在变量后面。放在变量前面时，我们可以称为前置递增（递减）运算符，放在变量后面时，我们可以称为后置递增（递减）运算符。

注意：递增和递减运算符必须和变量配合使用。

Increment operator

Pre-increment operator postincrement operator, when used alone, the same.

Pre-increment operator

Use formulas: the first from Canada, the return value

++num 前置递增，就是自加1，类似于 num =  num + 1，但是 ++num 写起来更简单。

使用口诀：**先自加，后返回值**

var  num = 10;
alert(++num + 10);   // 21

        // 1. 想要一个变量自己加1   num = num + 1 比较麻烦
        var num = 1;
        num = num + 1; // ++num
        num = num + 1;
        console.log(num); // 3
        // 2. 前置递增运算符  ++ 写在变量的前面
        var age = 10;
        ++age; // 类似于 age = age + 1
        console.log(age); // 11
        // 3. 先加1  后返回值
        var p = 10;
        console.log(++p + 10); // 21

Post-increment operator

After num ++ incrementation is self plus one, like num = num + 1, but num ++ much easier to write.

Use formulas: first return to the original value, after the self-imposed .

    var num = 10;
    num++; // num = num + 1    ++num;
    console.log(num); // 11
    // 1. 前置自增和后置自增如果单独使用 效果是一样的
    // 2. 后置自增 口诀：先返回原值 后自加1 
    var age = 10;
    // age++ + 10：age++：是一个表达式，先返回这个表达式的值10， 10 + 10 = 20。然后age再加1。
    console.log(age++ + 10); // 20
    console.log(age); // 11

        demo：前置递增、后置递增练习
        var a = 10;
        ++a; // ++a  11    a = 11
        var b = ++a + 2; // a = 12   ++a = 12
        console.log(b); // 14

        var c = 10;
        c++; // c++ 11  c = 11
        var d = c++ + 2; //  c++  = 11     c = 12
        console.log(d); // 13

        var e = 10;
        var f = e++ + ++e; // 1. e++ =  10  e = 11  2. e = 12  ++e = 12
        console.log(f); // 22
        // 后置自增  先表达式返回原值 后面变量再自加1

Pre-increment and post-increment Summary

Pre-increment and post-increment operator can simplify the preparation of the code, so that the variable value + 1 is simpler than before wording
When used alone, the same operation results
And when combined with other code, the results will be different
Rear: first original value calculation, since the addition (after ancestors hexyl)
Front: the first increase since, after the operation (first has descendants)
When developed, mostly using post increment / decrement, and an exclusive line of code, for example: num ++; or num--.

0103 increment and decrement operators

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