Go Syntax

Go Syntax Basics

Example: "hello world" program.

package main

//import the format package
import "fmt"

func main() {
   fmt.Println("Hello World")
}

Try it: go.dev/play

Comments

Comments are lines of text that explain code and are ignored by the Go compiler.

Single line comment: starts with two backslash symbols //

Multiple line comments: start with /* and end with */

Statements

• A statement is on a single line of code;
• The blocks of code are enclosed in curly brackets: {...};
• Semicolons are optional at the end of a line;
• Strings are separated by double quotes "" or ";
• Function is declared using "func" keyword;
• Strings are Unicode and the source code is also Unicode;
• Single line comment starts with two backslash symbols // like in C.
• Multiple line comments start with /* and end with */ like in C.

Variables

The var statement declares a list of variables. In variable declaration the type name is specified last. This is good since the type is optional. A var statement can be at package or function level. So we can have global variables and local variables.

Example.

//variables.go
package main

import "fmt"

var i, j int = 1, 2

func main() {
    var (
        c = true;
        p = false; 
        g = "no";
    )
	fmt.Println(i, j, c, p, g)
}

Try it: go.dev/play

Initial value

A var declaration can include one initializer for each variable. Initializer is usually a constant literal. If an initializer is present, the type can be omitted. The variable will take the type of the initializer. Read the example below to understand better this concept:

//file var_list.go
package main

import "fmt"

var i, j int = 1, 2

func main() {
    var c , p, g = true, false, "no"
	fmt.Println(i, j, c, p, g)
}

Constants

In Go it is good to use constants instead of regular variables to define numbers or other values that will not change during program execution.

• Constants are declared with the const keyword.
• Constants can be character, string, boolean, or numeric values.
• Constants must be initialized with literal using the assign symbol "=".

//file pub_con.go
package main

import "fmt"

const Pi = 3.14

func main() {
	const World = "世界"
	fmt.Println("Hello", World)
	fmt.Println("Happy", Pi, "Day")

	const Truth = true
	fmt.Println("Go rules?", Truth)
}

//file huge_con.go
package main

import "fmt"

const (
	// Create a huge number by shifting a 1 bit left 100 places.
	// In other words, the binary number that is 1 followed by 100 zeroes.
	Big = 1 << 100
	// Shift it right again 99 places, so we end up with 1<<1, or 2. 
    Small = Big >> 99
)

func needInt(x int) int { return x*10 + 1 }
func needFloat(x float64) float64 {
	return x * 0.1
}

func main() {
	fmt.Println(needInt(Small))
	fmt.Println(needFloat(Small))
	fmt.Println(needFloat(Big))
}

Try it: go.dev/play

Keywords

The following keywords are reserved and may not be used as identifiers.

Operators

In the following table we show all operators used in Go. Operators are similar to functions. There are binary operators that need left and right operands and there are unary operators that need only one operand: left or right.

Examples:

Operators are used to create expressions and statements. Here are some examples. We will study operators in details for every data type.

Read more:

• operators
• assignment

Packages & Imports

Every Go program is made up of packages. Programs start running in package "main". The main package also contains the function main(). Using the import statement one package can be used into another package. By convention, the package name is the same as the last element of the import path.

//file imp_pack.go
package main

import (
    "fmt"
    "math/rand"
)

func main() {
    fmt.Println("My favorite number is", rand.Intn(10))
}

In this instance, th package "math/rand" comprises files that begin with the statement "package rand".

Import

This code groups the imports into a parenthesis, "factored" import statement.

You can also write multiple import statements, like:

import "fmt"
import "math"

But it is good style to use the factored import statement.

Public elements

In Go, a name is exported automaticly if it begins with a capital letter. This is disruptive convention that makes Go different than Java. Where in Java class names start with capital letter, but Go do not have classes.

For example the "println()" function is using capital P so is fmt.Println() instead of fmt.println(). When the package "fmt" is imported only the capital letter functions and elements are accessible using dot notation.

Note: This convention is a bit strange but you get use to it.

Hello World Example

The classic "Hello World" program demonstrates the basic structure of a Go program:

package main

import "fmt"

func main() {
	fmt.Println("Hello, World!")
}

This is the simplest complete Go program you can write.