You Can Define a Constant Twice in a Block.
Variables are an of import programming concept to primary. They are symbols that stand up in for a value you're using in a programme.
This tutorial will cover some variable nuts and all-time practices for using them inside the Become programs you lot create.
Agreement Variables
In technical terms, a variable is assigning a storage location to a value that is tied to a symbolic name or identifier. We use the variable proper name to reference that stored value within a computer programme.
We can call back of a variable as a label that has a name on it, which y'all tie onto a value.
Permit's say we take an integer, 1032049348, and we desire to store it in a variable rather than continuously retype the long number over and once more. To achieve this, we tin can apply a name that's easy to recollect, like the variable i. To store a value in a variable, we use the following syntax:
i := 1032049348 We tin retrieve of this variable like a label that is tied to the value.
The characterization has the variable name i written on it, and is tied to the integer value 1032049348.
The phrase i := 1032049348 is a declaration and assignment statement that consists of a few parts:
- the variable name (
i) - the short variable declaration assignment (
:=) - the value that is being tied to the variable name (
1032049348) - the data type inferred by Go (
int)
We'll see later how to explicitly gear up the type in the side by side section.
Together, these parts make up the statement that sets the variable i equal to the value of the integer 1032049348.
Every bit soon every bit nosotros set a variable equal to a value, nosotros initialize or create that variable. One time we have done that, we are ready to use the variable instead of the value.
Once nosotros've set i equal to the value of 1032049348, we tin can use i in the identify of the integer, so let'southward impress information technology out:
packet chief import "fmt" func main ( ) { i := 1032049348 fmt. Println (i) } Output
1032049348 We tin can too chop-chop and easily do math by using variables. With i := 1032049348, we can subtract the integer value 813 with the following syntax:
fmt. Println (i - 813 ) Output
1032048535 In this instance, Go does the math for united states, subtracting 813 from the variable i to return the sum 1032048535.
Speaking of math, variables can be set equal to the result of a math equation. Y'all tin can also add two numbers together and store the value of the sum into the variable ten:
x := 76 + 145 You may accept noticed that this case looks like to algebra. In the same way that we use letters and other symbols to represent numbers and quantities inside formulas and equations, variables are symbolic names that stand for the value of a information type. For correct Go syntax, you'll need to make sure that your variable is on the left side of any equations.
Let's go ahead and print 10:
bundle primary import "fmt" func main ( ) { ten := 76 + 145 fmt. Println (x) } Output
221 Get returned the value 221 considering the variable 10 was ready equal to the sum of 76 and 145.
Variables can represent any information type, not but integers:
south := "Hello, World!" f := 45.06 b := five > nine // A Boolean value will return either true or false array := [ 4 ] string { "item_1" , "item_2" , "item_3" , "item_4" } slice := [ ] string { "one" , "2" , "iii" } m := map [ string ] string { "alphabetic character" : "g" , "number" : "seven" , "symbol" : "&" } If you print whatsoever of these variables, Go volition return what that variable is equivalent to. Let's work with the consignment statement for the cord slice data type:
package main import "fmt" func main ( ) { slice := [ ] cord { "one" , "2" , "three" } fmt. Println (slice) } Output
[i two iii] We assigned the slice value of []cord{"1", "ii", "three"} to the variable slice, and then used the fmt.Println part to print out that value by calling piece.
Variables work by etching out a little expanse of memory within your estimator that accepts specified values that are and then associated with that space.
Declaring Variables
In Go, there are several means to declare a variable, and in some cases, more than i way to declare the exact same variable and value.
We can declare a variable chosen i of information type int without initialization. This means we will declare a space to put a value, but not give information technology an initial value:
var i int This creates a variable alleged equally i of data type int.
We tin initialize the value by using the equal (=) operator, similar in the following example:
var i int = 1 In Go, both of these forms of declaration are chosen long variable declarations.
We can as well use short variable declaration:
i := 1 In this case, we accept a variable called i, and a data blazon of int. When we don't specify a information blazon, Get volition infer the data type.
With the three ways to declare variables, the Get community has adopted the post-obit idioms:
-
Merely use long form,
var i int, when y'all're not initializing the variable. -
Use brusque course,
i := i, when declaring and initializing. -
If you lot did non want Go to infer your data type, but y'all still want to use short variable proclamation, you can wrap your value in your desired type, with the following syntax:
i := int64 ( i ) Information technology's not considered idiomatic in Go to use the long variable proclamation form when we're initializing the value:
var i int = i It's skilful practice to follow how the Go customs typically declares variables so that others tin seamlessly read your programs.
Zero Values
All born types have a zero value. Whatsoever allocated variable is usable even if it never has a value assigned. We can run across the nada values for the post-obit types:
package main import "fmt" func main ( ) { var a int var b string var c float64 var d bool fmt. Printf ( "var a %T = %+v\n" , a, a) fmt. Printf ( "var b %T = %q\northward" , b, b) fmt. Printf ( "var c %T = %+v\due north" , c, c) fmt. Printf ( "var d %T = %+v\n\n" , d, d) } Output
var a int = 0 var b string = "" var c float64 = 0 var d bool = false We used the %T verb in the fmt.Printf argument. This tells the office to print the data blazon for the variable.
In Go, because all values have a naught value, we can't have undefined values like another languages. For instance, a boolean in some languages could be undefined, true, or simulated, which allows for three states to the variable. In Go, nosotros tin can't have more than two states for a boolean value.
Naming Variables: Rules and Style
The naming of variables is quite flexible, but there are some rules to keep in mind:
- Variable names must only be one word (as in no spaces).
- Variable names must be made up of only letters, numbers, and underscores (
_). - Variable names cannot begin with a number.
Following these rules, allow'southward look at both valid and invalid variable names:
| Valid | Invalid | Why Invalid |
|---|---|---|
userName | user-name | Hyphens are not permitted |
name4 | 4name | Cannot begin with a number |
user | $user | Cannot utilise symbols |
userName | user name | Cannot be more than one word |
Furthermore, keep in listen when naming variables that they are case sensitive. These names userName, USERNAME, UserName, and uSERnAME are all completely different variables. Information technology's all-time practice to avoid using similar variable names within a program to ensure that both you and your collaborators—electric current and future—tin keep your variables straight.
While variables are case sensitive, the example of the first letter of a variable has special significant in Go. If a variable starts with an majuscule alphabetic character, then that variable is attainable outside the bundle it was alleged in (or exported). If a variable starts with a lowercase alphabetic character, then information technology is just available within the package it is declared in.
var Email string var password string Electronic mail starts with an capital letter letter and can be accessed past other packages. password starts with a lowercase letter of the alphabet, and is just accessible within the package information technology is declared in.
It is common in Get to utilise very terse (or short) variable names. Given the choice between using userName and user for a variable, information technology would be idiomatic to choose user.
Scope likewise plays a office in the terseness of the variable proper name. The rule is that the smaller the scope the variable exists in, the smaller the variable name:
names := [ ] string { "Mary" , "John" , "Bob" , "Anna" } for i, n := range names { fmt. Printf ( "alphabetize: %d = %q\n" , i, n) } We use the variable names in a larger scope, and so it would exist mutual to give it a more meaningful name to assist retrieve what it means in the plan. However, we utilise the i and n variables immediately in the side by side line of code, and and so exercise not use them again… Because of this, it won't confuse someone reading the code about where the variables are used, or what they hateful.
Next, let'south cover some notes about variable style. The way is to utilise MixedCaps or mixedCaps rather than underscores for multi-give-and-take names.
| Conventional Style | Unconventional Way | Why Anarchistic |
|---|---|---|
userName | user_name | Underscores are not conventional |
i | alphabetize | prefer i over index as it is shorter |
serveHTTP | serveHttp | acronyms should be capitalized |
The most of import thing almost style is to be consistent, and that the team you work on agrees to the style.
Reassigning Variables
Every bit the give-and-take "variable" implies, we tin can change Go variables readily. This ways that we tin can connect a dissimilar value with a previously assigned variable through reassignment. Existence able to reassign is useful considering throughout the class of a program nosotros may need to have user-generated values into already initialized variables. We may likewise need to change the assignment to something previously divers.
Knowing that we tin readily reassign a variable can exist useful when working on a large program that someone else wrote, and it isn't articulate what variables are already divers.
Let'south assign the value of 76 to a variable called i of type int, then assign it a new value of 42:
package main import "fmt" func chief ( ) { i := 76 fmt. Println (i) i = 42 fmt. Println (i) } Output
76 42 This example shows that we can first assign the variable i with the value of an integer, and then reassign the variable i assigning information technology this fourth dimension with the value of 42.
Note: When you declare and initialize a variable, you can use :=, however, when you want to simply alter the value of an already declared variable, you only demand to use the equal operator (=).
Considering Become is a typed linguistic communication, we tin can't assign one type to another. For instance, we tin't assign the value "Sammy" to a variable of blazon int:
i := 72 i = "Sammy" Trying to assign different types to each other volition upshot in a compile-fourth dimension error:
Output
cannot utilize "Sammy" (type string) every bit type int in assignment Go volition not allow us to use a variable proper name more than once:
var s string var s string Output
s redeclared in this block If we effort to utilize short variable declaration more than once for the aforementioned variable name we'll likewise receive a compilation error. This can happen past mistake, so understanding what the error message means is helpful:
i := 5 i := 10 Output
no new variables on left side of := Similarly to variable annunciation, giving consideration to the naming of your variables will improve the readability of your program for you, and others, when you lot revisit it in the hereafter.
Multiple Assignment
Go also allows us to assign several values to several variables within the aforementioned line. Each of these values can be of a different data type:
j, k, l := "shark" , ii.05 , 15 fmt. Println (j) fmt. Println (k) fmt. Println (l) Output
shark 2.05 15 In this case, the variable j was assigned to the string "shark", the variable grand was assigned to the float 2.05, and the variable 50 was assigned to the integer 15.
This approach to assigning multiple variables to multiple values in one line can keep the number of lines in your code downwards. However, information technology'due south important to not compromise readability for fewer lines of code.
Global and Local Variables
When using variables within a programme, information technology is of import to keep variable telescopic in mind. A variable'south scope refers to the detail places it is accessible from inside the lawmaking of a given program. This is to say that non all variables are attainable from all parts of a given programme—some variables will be global and some will be local.
Global variables exist outside of functions. Local variables exist within functions.
Let'southward take a look at global and local variables in action:
package principal import "fmt" var g = "global" func printLocal ( ) { fifty := "local" fmt. Println (fifty) } func primary ( ) { printLocal ( ) fmt. Println (chiliad) } Output
local global Here nosotros use var g = "global" to create a global variable outside of the part. Then nosotros ascertain the function printLocal(). Inside of the function a local variable called l is assigned and then printed out. The program ends by calling printLocal() and then press the global variable m.
Considering m is a global variable, nosotros tin refer to it in printLocal(). Let'due south modify the previous plan to practice that:
package main import "fmt" var thou = "global" func printLocal ( ) { fifty := "local" fmt. Println (l) fmt. Println (k) } func main ( ) { printLocal ( ) fmt. Println (g) } Output
local global global We get-go by declaring a global variable g, var g = "global". In the main role, we call the function printLocal, which declares a local variable l and prints it out, fmt.Println(50). Then, printLocal prints out the global variable grand, fmt.Println(g). Even though g wasn't defined within printLocal, it could all the same exist accessed because it was declared in a global telescopic. Finally, the main function prints out grand every bit well.
Now allow's endeavour to call the local variable outside of the function:
parcel main import "fmt" var g = "global" func printLocal ( ) { l := "local" fmt. Println (l) } func primary ( ) { fmt. Println (l) } Output
undefined: l We can't use a local variable outside of the function it is assigned in. If you endeavor to do and so, you'll receive a undefined error when you compile.
Let's look at another example where nosotros utilise the same variable name for a global variable and a local variable:
package main import "fmt" var num1 = 5 func printNumbers ( ) { num1 := 10 num2 := 7 fmt. Println (num1) fmt. Println (num2) } func main ( ) { printNumbers ( ) fmt. Println (num1) } Output
x 7 5 In this program, we declared the num1 variable twice. First, we alleged num1 at the global scope, var num1 = 5, and once more within the local scope of the printNumbers function, num1 := 10. When we print num1 from the main program, we see the value of 5 printed out. This is considering main only sees the global variable annunciation. Withal, when we print out num1 from the printNumbers office, it sees the local announcement, and will impress out the value of x. Even though printNumbers creates a new variable called num1 and assigned information technology a value of 10, it does not affect the global instance of num1 with the value of 5.
When working with variables, you also need to consider what parts of your plan will need admission to each variables; adopting a global or local variable accordingly. Across Go programs, you'll find that local variables are typically more common.
Constants
Constants are like variables, except they tin't be modified once they have been declared. Constants are useful for defining a value that will be used more once in your program, but shouldn't exist able to change.
For instance, if nosotros wanted to declare the tax rate for a shopping cart system, nosotros could use a constant and and so calculate tax in different areas of our program. At some point in the hereafter, if the tax charge per unit changes, we just take to change that value in one spot in our program. If we used a variable, it is possible that nosotros might accidentally modify the value somewhere in our programme, which would consequence in an improper calculation.
To declare a constant, we can use the post-obit syntax:
const shark = "Sammy" fmt. Println (shark) Output
Sammy If we effort to alter a abiding after information technology was declared, we'll get a compile-time fault:
Output
cannot assign to shark Constants can be untyped. This can be useful when working with numbers such as integer-blazon data. If the constant is untyped, it is explicitly converted, where typed constants are not. Let's run across how we can use constants:
package main import "fmt" const ( year = 365 leapYear = int32 ( 366 ) ) func principal ( ) { hours := 24 minutes := int32 ( lx ) fmt. Println (hours * year) fmt. Println (minutes * yr) fmt. Println (minutes * leapYear) } Output
8760 21900 21960 If you declare a constant with a blazon, it volition be that exact type. Hither when we declare the constant leapYear, we define it as information blazon int32. Therefore it is a typed abiding, which ways information technology can just operate with int32 data types. The year constant we declare with no type, so it is considered untyped. Because of this, yous can use it with any integer information type.
When hours was defined, it inferred that it was of blazon int because nosotros did not explicitly give it a type, hours := 24. When we declared minutes, we explicitly alleged information technology equally an int32, minutes := int32(60).
Now allow's walk through each adding and why it works:
hours * year In this case, hours is an int, and years is untyped. When the programme compiles, it explicitly converts years to an int, which allows the multiplication operation to succeed.
minutes * twelvemonth In this case, minutes is an int32, and year is untyped. When the plan compiles, it explicitly converts years to an int32, which allows the multiplication operation to succeed.
minutes * leapYear In this case, minutes is an int32, and leapYear is a typed abiding of int32. At that place is nothing for the compiler to do this time every bit both variables are already of the same type.
If nosotros try to multiply two types that are typed and not uniform, the plan will not compile:
fmt. Println (hours * leapYear) Output
invalid performance: hours * leapYear (mismatched types int and int32) In this case, hours was inferred equally an int, and leapYear was explicitly alleged every bit an int32. Because Become is a typed linguistic communication, an int and an int32 are not compatible for mathematical operations. To multiply them, you lot would need to catechumen i to a int32 or an int.
Conclusion
In this tutorial nosotros reviewed some of the mutual use cases of variables inside Go. Variables are an of import building cake of programming, serving as symbols that stand in for the value of a data blazon we use in a program.
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Source: https://www.digitalocean.com/community/tutorials/how-to-use-variables-and-constants-in-go
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