Golang Learning Notes 3--constants and operators

This is a creation in Article, where the information may have evolved or changed.

1. Definition of constants

• The value of the constant is confirmed at compile time

• Constants are defined in the same format as variables

• The right side of the equal sign must be a constant or constant expression

• A function in a constant expression must be a built-in function

//定义单个常量constint1const"A"const (    "123"    len(text)    20)//同时定义多个变量const1"2""3"const (    "456"len(text2),  10)

2. Initialization rules for constants

• When defining a constant group, an expression that uses the upstream if the initial value is not provided

var1const (    b  = a    //此时报错，因为全局变量在编译时不能确定值，常量必须是编译时能确定值的或使用内置函数获得的值(eg:len()) )  const (    "A"    b    c    //此时 a,b,c都为"A" )  const (    1"A"    c, d    //a,c为1，b,d为"A"。此时注意下行的常量个数必须与上行数量保持一致 )

3. Enumeration of constants

• Using the same expression does not mean that you have the same value

• Iota is a constant counter, starting with 0 and automatically incrementing 1 for each of the 1 constants defined in the group.

• The effect of enumerations can be achieved by initializing rules with iota

• Iota resets to 0 for every const keyword encountered

const (    "A"    b    iota    d        //d的值为3，因为在常量组中，定义了4个变量所以iota计数器从0开始计数4次，所以为3)

4. Operators

//优先级从高到低        *  /  %  <<  >>  &  &^ =  -  |  ^     ==  !=  <  <=  >= > && ||

Example:

/*   10 binary: 1011 second  --------- & 0010 = 2 (Two of them are 1 for 1)   | 1111 = 15 (one is 1 is 1)  ^ 1101 = 13 (two only one is 1 is 1)  $^ 0100 = 4 (the second is 1) is 0, otherwise the same as the first)  */